diff --git a/toolchain/check/import_cpp.cpp b/toolchain/check/import_cpp.cpp
index 8874e5075f62..ce11c7eb3b3e 100644
--- a/toolchain/check/import_cpp.cpp
+++ b/toolchain/check/import_cpp.cpp
@@ -1125,9 +1125,8 @@ static auto MapNonWrapperType(Context& context, SemIR::LocId loc_id,
 }
 
 // Maps a qualified C++ type to a Carbon type.
-static auto MapQualifiedType(Context& context, SemIR::LocId loc_id,
-                             clang::QualType type, TypeExpr type_expr)
-    -> TypeExpr {
+static auto MapQualifiedType(Context& context, clang::QualType type,
+                             TypeExpr type_expr) -> TypeExpr {
   auto quals = type.getQualifiers();
 
   if (quals.hasConst()) {
@@ -1139,28 +1138,22 @@ static auto MapQualifiedType(Context& context, SemIR::LocId loc_id,
 
   // TODO: Support other qualifiers.
   if (!quals.empty()) {
-    context.TODO(loc_id, llvm::formatv("Unsupported: qualified type: {0}",
-                                       type.getAsString()));
-    return {.inst_id = SemIR::ErrorInst::TypeInstId,
-            .type_id = SemIR::ErrorInst::TypeId};
+    return {.inst_id = SemIR::TypeInstId::None, .type_id = SemIR::TypeId::None};
   }
 
   return type_expr;
 }
 
 // Maps a C++ pointer type to a Carbon pointer type.
-static auto MapPointerType(Context& context, SemIR::LocId loc_id,
-                           clang::QualType type, TypeExpr pointee_type_expr)
-    -> TypeExpr {
+static auto MapPointerType(Context& context, clang::QualType type,
+                           TypeExpr pointee_type_expr) -> TypeExpr {
   CARBON_CHECK(type->isPointerType());
 
   if (auto nullability = type->getNullability();
       !nullability.has_value() ||
       *nullability != clang::NullabilityKind::NonNull) {
-    context.TODO(loc_id, llvm::formatv("Unsupported: nullable pointer: {0}",
-                                       type.getAsString()));
-    return {.inst_id = SemIR::ErrorInst::TypeInstId,
-            .type_id = SemIR::ErrorInst::TypeId};
+    // TODO: Support nullable pointers.
+    return {.inst_id = SemIR::TypeInstId::None, .type_id = SemIR::TypeId::None};
   }
 
   SemIR::TypeId pointer_type_id =
@@ -1197,9 +1190,9 @@ static auto MapType(Context& context, SemIR::LocId loc_id, clang::QualType type)
     }
 
     if (wrapper.hasQualifiers()) {
-      mapped = MapQualifiedType(context, loc_id, wrapper, mapped);
+      mapped = MapQualifiedType(context, wrapper, mapped);
     } else if (wrapper->isPointerType()) {
-      mapped = MapPointerType(context, loc_id, wrapper, mapped);
+      mapped = MapPointerType(context, wrapper, mapped);
     } else {
       CARBON_FATAL("Unexpected wrapper type {0}", wrapper.getAsString());
     }
@@ -1656,11 +1649,12 @@ static auto ImportDeclAfterDependencies(Context& context, SemIR::LocId loc_id,
     return ImportNamespaceDecl(context, clang_namespace_decl);
   }
   if (auto* type_decl = dyn_cast<clang::TypeDecl>(clang_decl)) {
-    auto type = type_decl->getASTContext().getTypeDeclType(type_decl);
+    auto type = clang_decl->getASTContext().getTypeDeclType(type_decl);
     auto type_inst_id = MapType(context, loc_id, type).inst_id;
     if (!type_inst_id.has_value()) {
-      context.TODO(loc_id, llvm::formatv("Unsupported: Type declaration: {0}",
-                                         type.getAsString()));
+      context.TODO(AddImportIRInst(context.sem_ir(), type_decl->getLocation()),
+                   llvm::formatv("Unsupported: Type declaration: {0}",
+                                 type.getAsString()));
       return SemIR::ErrorInst::InstId;
     }
     return type_inst_id;
@@ -1672,13 +1666,15 @@ static auto ImportDeclAfterDependencies(Context& context, SemIR::LocId loc_id,
         existing_inst_id.has_value()) {
       return existing_inst_id;
     }
-    context.TODO(loc_id, "Unsupported: Unhandled kind of field declaration");
-    return SemIR::InstId::None;
+    context.TODO(AddImportIRInst(context.sem_ir(), clang_decl->getLocation()),
+                 "Unsupported: field declaration has unhandled type or kind");
+    return SemIR::ErrorInst::InstId;
   }
 
-  context.TODO(loc_id, llvm::formatv("Unsupported: Declaration type {0}",
-                                     clang_decl->getDeclKindName()));
-  return SemIR::InstId::None;
+  context.TODO(AddImportIRInst(context.sem_ir(), clang_decl->getLocation()),
+               llvm::formatv("Unsupported: Declaration type {0}",
+                             clang_decl->getDeclKindName()));
+  return SemIR::ErrorInst::InstId;
 }
 
 // Imports a declaration from Clang to Carbon. If successful, returns the
diff --git a/toolchain/check/testdata/interop/cpp/class/class.carbon b/toolchain/check/testdata/interop/cpp/class/class.carbon
index bdcf5be49074..691e846d4778 100644
--- a/toolchain/check/testdata/interop/cpp/class/class.carbon
+++ b/toolchain/check/testdata/interop/cpp/class/class.carbon
@@ -121,18 +121,15 @@ class Bar {
 
 library "[[@TEST_NAME]]";
 
+// CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+4]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./static_data_member.h:4:15: error: semantics TODO: `Unsupported: Declaration type Var` [SemanticsTodo]
+// CHECK:STDERR:   static Bar* foo;
+// CHECK:STDERR:               ^
 import Cpp library "static_data_member.h";
 
 fn MyF() {
   //@dump-sem-ir-begin
-  // CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+11]]:23: error: semantics TODO: `Unsupported: Declaration type Var` [SemanticsTodo]
-  // CHECK:STDERR:   let bar: Cpp.Bar* = Cpp.Bar.foo();
-  // CHECK:STDERR:                       ^~~~~~~~~~~
-  // CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+8]]:23: note: in `Cpp` name lookup for `foo` [InCppNameLookup]
-  // CHECK:STDERR:   let bar: Cpp.Bar* = Cpp.Bar.foo();
-  // CHECK:STDERR:                       ^~~~~~~~~~~
-  // CHECK:STDERR:
-  // CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+4]]:23: error: member name `foo` not found in `Cpp.Bar` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+4]]:23: note: in `Cpp` name lookup for `foo` [InCppNameLookup]
   // CHECK:STDERR:   let bar: Cpp.Bar* = Cpp.Bar.foo();
   // CHECK:STDERR:                       ^~~~~~~~~~~
   // CHECK:STDERR:
@@ -224,17 +221,14 @@ class Bar {};
 
 library "[[@TEST_NAME]]";
 
+// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+4]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./template.h:3:7: error: semantics TODO: `Unsupported: Declaration type ClassTemplate` [SemanticsTodo]
+// CHECK:STDERR: class Bar {};
+// CHECK:STDERR:       ^
 import Cpp library "template.h";
 
 //@dump-sem-ir-begin
-// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+11]]:13: error: semantics TODO: `Unsupported: Declaration type ClassTemplate` [SemanticsTodo]
-// CHECK:STDERR: fn MyF(bar: Cpp.Bar*);
-// CHECK:STDERR:             ^~~~~~~
-// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+8]]:13: note: in `Cpp` name lookup for `Bar` [InCppNameLookup]
-// CHECK:STDERR: fn MyF(bar: Cpp.Bar*);
-// CHECK:STDERR:             ^~~~~~~
-// CHECK:STDERR:
-// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+4]]:13: error: member name `Bar` not found in `Cpp` [MemberNameNotFoundInInstScope]
+// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+4]]:13: note: in `Cpp` name lookup for `Bar` [InCppNameLookup]
 // CHECK:STDERR: fn MyF(bar: Cpp.Bar*);
 // CHECK:STDERR:             ^~~~~~~
 // CHECK:STDERR:
@@ -394,13 +388,13 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT:   name_binding_decl {
 // CHECK:STDOUT:     %bar.patt: %pattern_type = binding_pattern bar [concrete]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   %Cpp.ref.loc19_23: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
-// CHECK:STDOUT:   %Bar.ref.loc19_26: type = name_ref Bar, imports.%Bar.decl [concrete = constants.%Bar]
+// CHECK:STDOUT:   %Cpp.ref.loc16_23: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   %Bar.ref.loc16_26: type = name_ref Bar, imports.%Bar.decl [concrete = constants.%Bar]
 // CHECK:STDOUT:   %foo.ref: <error> = name_ref foo, <error> [concrete = <error>]
-// CHECK:STDOUT:   %.loc19: type = splice_block %ptr [concrete = constants.%ptr.f68] {
-// CHECK:STDOUT:     %Cpp.ref.loc19_12: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
-// CHECK:STDOUT:     %Bar.ref.loc19_15: type = name_ref Bar, imports.%Bar.decl [concrete = constants.%Bar]
-// CHECK:STDOUT:     %ptr: type = ptr_type %Bar.ref.loc19_15 [concrete = constants.%ptr.f68]
+// CHECK:STDOUT:   %.loc16: type = splice_block %ptr [concrete = constants.%ptr.f68] {
+// CHECK:STDOUT:     %Cpp.ref.loc16_12: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:     %Bar.ref.loc16_15: type = name_ref Bar, imports.%Bar.decl [concrete = constants.%Bar]
+// CHECK:STDOUT:     %ptr: type = ptr_type %Bar.ref.loc16_15 [concrete = constants.%ptr.f68]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %bar: %ptr.f68 = bind_name bar, <error> [concrete = <error>]
 // CHECK:STDOUT:   <elided>
@@ -584,7 +578,7 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT:
 // CHECK:STDOUT: imports {
 // CHECK:STDOUT:   %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
-// CHECK:STDOUT:     .Bar = <poisoned>
+// CHECK:STDOUT:     .Bar = <error>
 // CHECK:STDOUT:     import Cpp//...
 // CHECK:STDOUT:   }
 // CHECK:STDOUT: }
@@ -595,7 +589,7 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT:     %bar.param_patt: <error> = value_param_pattern %bar.patt, call_param0 [concrete]
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %bar.param: <error> = value_param call_param0
-// CHECK:STDOUT:     %.loc18: type = splice_block %ptr [concrete = <error>] {
+// CHECK:STDOUT:     %.loc15: type = splice_block %ptr [concrete = <error>] {
 // CHECK:STDOUT:       %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
 // CHECK:STDOUT:       %Bar.ref: <error> = name_ref Bar, <error> [concrete = <error>]
 // CHECK:STDOUT:       %ptr: type = ptr_type <error> [concrete = <error>]
diff --git a/toolchain/check/testdata/interop/cpp/class/field.carbon b/toolchain/check/testdata/interop/cpp/class/field.carbon
index 0e0a0f520f74..68d94bebc94e 100644
--- a/toolchain/check/testdata/interop/cpp/class/field.carbon
+++ b/toolchain/check/testdata/interop/cpp/class/field.carbon
@@ -123,35 +123,29 @@ fn G(s: Cpp.Union) -> i32 {
 
 library "[[@TEST_NAME]]";
 
+// CHECK:STDERR: fail_todo_use_bitfields.carbon:[[@LINE+4]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./with_bitfields.h:4:7: error: semantics TODO: `Unsupported: field declaration has unhandled type or kind` [SemanticsTodo]
+// CHECK:STDERR:   int b : 2;
+// CHECK:STDERR:       ^
 import Cpp library "with_bitfields.h";
 
 fn F(s: Cpp.Struct) -> i32 {
   //@dump-sem-ir-begin
-  // CHECK:STDERR: fail_todo_use_bitfields.carbon:[[@LINE+11]]:10: error: semantics TODO: `Unsupported: Unhandled kind of field declaration` [SemanticsTodo]
-  // CHECK:STDERR:   return s.b;
-  // CHECK:STDERR:          ^~~
   // CHECK:STDERR: fail_todo_use_bitfields.carbon:[[@LINE+8]]:10: note: in `Cpp` name lookup for `b` [InCppNameLookup]
   // CHECK:STDERR:   return s.b;
   // CHECK:STDERR:          ^~~
   // CHECK:STDERR:
-  // CHECK:STDERR: fail_todo_use_bitfields.carbon:[[@LINE+4]]:10: error: member name `b` not found in `Cpp.Struct` [MemberNameNotFoundInInstScope]
-  // CHECK:STDERR:   return s.b;
-  // CHECK:STDERR:          ^~~
-  // CHECK:STDERR:
+  // CHECK:STDERR: fail_todo_use_bitfields.carbon:[[@LINE-8]]:10: in file included here [InCppInclude]
+  // CHECK:STDERR: ./with_bitfields.h:9:7: error: semantics TODO: `Unsupported: field declaration has unhandled type or kind` [SemanticsTodo]
+  // CHECK:STDERR:   int d : 3;
+  // CHECK:STDERR:       ^
   return s.b;
   //@dump-sem-ir-end
 }
 
 fn G(s: Cpp.Union) -> i32 {
   //@dump-sem-ir-begin
-  // CHECK:STDERR: fail_todo_use_bitfields.carbon:[[@LINE+11]]:10: error: semantics TODO: `Unsupported: Unhandled kind of field declaration` [SemanticsTodo]
-  // CHECK:STDERR:   return s.d;
-  // CHECK:STDERR:          ^~~
-  // CHECK:STDERR: fail_todo_use_bitfields.carbon:[[@LINE+8]]:10: note: in `Cpp` name lookup for `d` [InCppNameLookup]
-  // CHECK:STDERR:   return s.d;
-  // CHECK:STDERR:          ^~~
-  // CHECK:STDERR:
-  // CHECK:STDERR: fail_todo_use_bitfields.carbon:[[@LINE+4]]:10: error: member name `d` not found in `Cpp.Union` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR: fail_todo_use_bitfields.carbon:[[@LINE+4]]:10: note: in `Cpp` name lookup for `d` [InCppNameLookup]
   // CHECK:STDERR:   return s.d;
   // CHECK:STDERR:          ^~~
   // CHECK:STDERR:
@@ -159,6 +153,72 @@ fn G(s: Cpp.Union) -> i32 {
   //@dump-sem-ir-end
 }
 
+// --- unsupported_members.h
+
+struct UnsupportedMembers {
+  // Volatile is not supported.
+  volatile int is_volatile;
+  // Nullable pointers are not supported.
+  int *is_nullable;
+  // References are not supported.
+  int &is_reference;
+  // But this should be fine.
+  int integer;
+};
+
+void Consume(UnsupportedMembers);
+
+// --- supported_members_in_type_with_unsupported_members.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "unsupported_members.h";
+
+fn Test(m: Cpp.UnsupportedMembers*) {
+  // OK: Can still access supported members.
+  m->integer = 42;
+  // OK: Can still pass the class to a C++ function.
+  Cpp.Consume(*m);
+}
+
+// --- fail_use_unsupported_members.carbon
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: fail_use_unsupported_members.carbon:[[@LINE+4]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./unsupported_members.h:4:16: error: semantics TODO: `Unsupported: field declaration has unhandled type or kind` [SemanticsTodo]
+// CHECK:STDERR:   volatile int is_volatile;
+// CHECK:STDERR:                ^
+import Cpp library "unsupported_members.h";
+
+fn Test(m: Cpp.UnsupportedMembers*) {
+  // CHECK:STDERR: fail_use_unsupported_members.carbon:[[@LINE+8]]:16: note: in `Cpp` name lookup for `is_volatile` [InCppNameLookup]
+  // CHECK:STDERR:   let a: i32 = m->is_volatile;
+  // CHECK:STDERR:                ^~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  // CHECK:STDERR: fail_use_unsupported_members.carbon:[[@LINE-7]]:10: in file included here [InCppInclude]
+  // CHECK:STDERR: ./unsupported_members.h:6:8: error: semantics TODO: `Unsupported: field declaration has unhandled type or kind` [SemanticsTodo]
+  // CHECK:STDERR:   int *is_nullable;
+  // CHECK:STDERR:        ^
+  let a: i32 = m->is_volatile;
+
+  // CHECK:STDERR: fail_use_unsupported_members.carbon:[[@LINE+8]]:17: note: in `Cpp` name lookup for `is_nullable` [InCppNameLookup]
+  // CHECK:STDERR:   let b: i32 = *m->is_nullable;
+  // CHECK:STDERR:                 ^~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  // CHECK:STDERR: fail_use_unsupported_members.carbon:[[@LINE-17]]:10: in file included here [InCppInclude]
+  // CHECK:STDERR: ./unsupported_members.h:8:8: error: semantics TODO: `Unsupported: field declaration has unhandled type or kind` [SemanticsTodo]
+  // CHECK:STDERR:   int &is_reference;
+  // CHECK:STDERR:        ^
+  let b: i32 = *m->is_nullable;
+
+  // CHECK:STDERR: fail_use_unsupported_members.carbon:[[@LINE+4]]:16: note: in `Cpp` name lookup for `is_reference` [InCppNameLookup]
+  // CHECK:STDERR:   let c: i32 = m->is_reference;
+  // CHECK:STDERR:                ^~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  let c: i32 = m->is_reference;
+}
+
 // CHECK:STDOUT: --- use_struct_fields.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
diff --git a/toolchain/check/testdata/interop/cpp/class/method.carbon b/toolchain/check/testdata/interop/cpp/class/method.carbon
index 30014c4e9ee7..6a2a08c301e1 100644
--- a/toolchain/check/testdata/interop/cpp/class/method.carbon
+++ b/toolchain/check/testdata/interop/cpp/class/method.carbon
@@ -57,18 +57,13 @@ fn Value(v: Cpp.HasQualifiers) {
   v.plain();
 
   // TODO: This should remain invalid once we support `volatile`.
-  // CHECK:STDERR: fail_bad_object_param_qualifiers_by_value.carbon:[[@LINE+12]]:3: error: semantics TODO: `Unsupported: qualified type: volatile struct HasQualifiers` [SemanticsTodo]
+  // CHECK:STDERR: fail_bad_object_param_qualifiers_by_value.carbon:[[@LINE+7]]:3: error: semantics TODO: `Unsupported: object parameter type: volatile struct HasQualifiers` [SemanticsTodo]
   // CHECK:STDERR:   v.volatile_this();
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~
-  // CHECK:STDERR: fail_bad_object_param_qualifiers_by_value.carbon:[[@LINE+9]]:3: note: in `Cpp` name lookup for `volatile_this` [InCppNameLookup]
+  // CHECK:STDERR: fail_bad_object_param_qualifiers_by_value.carbon:[[@LINE+4]]:3: note: in `Cpp` name lookup for `volatile_this` [InCppNameLookup]
   // CHECK:STDERR:   v.volatile_this();
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~
   // CHECK:STDERR:
-  // CHECK:STDERR: fail_bad_object_param_qualifiers_by_value.carbon:[[@LINE+5]]:3: error: `addr self` method cannot be invoked on a value [AddrSelfIsNonRef]
-  // CHECK:STDERR:   v.volatile_this();
-  // CHECK:STDERR:   ^
-  // CHECK:STDERR: fail_bad_object_param_qualifiers_by_value.carbon: note: initializing function parameter [InCallToFunctionParam]
-  // CHECK:STDERR:
   v.volatile_this();
 
   // CHECK:STDERR: fail_bad_object_param_qualifiers_by_value.carbon:[[@LINE+5]]:3: error: `addr self` method cannot be invoked on a value [AddrSelfIsNonRef]
@@ -105,7 +100,7 @@ import Cpp library "object_param_qualifiers.h";
 
 fn Ref(p: Cpp.HasQualifiers*) {
   // TODO: This should eventually be accepted if we support `volatile`.
-  // CHECK:STDERR: fail_todo_bad_object_param_qualifiers_by_ref.carbon:[[@LINE+7]]:3: error: semantics TODO: `Unsupported: qualified type: volatile struct HasQualifiers` [SemanticsTodo]
+  // CHECK:STDERR: fail_todo_bad_object_param_qualifiers_by_ref.carbon:[[@LINE+7]]:3: error: semantics TODO: `Unsupported: object parameter type: volatile struct HasQualifiers` [SemanticsTodo]
   // CHECK:STDERR:   p->volatile_this();
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_todo_bad_object_param_qualifiers_by_ref.carbon:[[@LINE+4]]:3: note: in `Cpp` name lookup for `volatile_this` [InCppNameLookup]
diff --git a/toolchain/check/testdata/interop/cpp/class/struct.carbon b/toolchain/check/testdata/interop/cpp/class/struct.carbon
index ff4bf135ff60..f7c69b2a71e9 100644
--- a/toolchain/check/testdata/interop/cpp/class/struct.carbon
+++ b/toolchain/check/testdata/interop/cpp/class/struct.carbon
@@ -119,18 +119,15 @@ struct Bar {
 
 library "[[@TEST_NAME]]";
 
+// CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+4]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./static_data_member.h:3:24: error: semantics TODO: `Unsupported: Declaration type Var` [SemanticsTodo]
+// CHECK:STDERR:   static Bar* _Nonnull foo;
+// CHECK:STDERR:                        ^
 import Cpp library "static_data_member.h";
 
 fn MyF() {
   //@dump-sem-ir-begin
-  // CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+11]]:23: error: semantics TODO: `Unsupported: Declaration type Var` [SemanticsTodo]
-  // CHECK:STDERR:   let bar: Cpp.Bar* = Cpp.Bar.foo();
-  // CHECK:STDERR:                       ^~~~~~~~~~~
-  // CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+8]]:23: note: in `Cpp` name lookup for `foo` [InCppNameLookup]
-  // CHECK:STDERR:   let bar: Cpp.Bar* = Cpp.Bar.foo();
-  // CHECK:STDERR:                       ^~~~~~~~~~~
-  // CHECK:STDERR:
-  // CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+4]]:23: error: member name `foo` not found in `Cpp.Bar` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+4]]:23: note: in `Cpp` name lookup for `foo` [InCppNameLookup]
   // CHECK:STDERR:   let bar: Cpp.Bar* = Cpp.Bar.foo();
   // CHECK:STDERR:                       ^~~~~~~~~~~
   // CHECK:STDERR:
@@ -212,17 +209,14 @@ struct Bar {};
 
 library "[[@TEST_NAME]]";
 
+// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+4]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./template.h:3:8: error: semantics TODO: `Unsupported: Declaration type ClassTemplate` [SemanticsTodo]
+// CHECK:STDERR: struct Bar {};
+// CHECK:STDERR:        ^
 import Cpp library "template.h";
 
 //@dump-sem-ir-begin
-// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+11]]:13: error: semantics TODO: `Unsupported: Declaration type ClassTemplate` [SemanticsTodo]
-// CHECK:STDERR: fn MyF(bar: Cpp.Bar*);
-// CHECK:STDERR:             ^~~~~~~
-// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+8]]:13: note: in `Cpp` name lookup for `Bar` [InCppNameLookup]
-// CHECK:STDERR: fn MyF(bar: Cpp.Bar*);
-// CHECK:STDERR:             ^~~~~~~
-// CHECK:STDERR:
-// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+4]]:13: error: member name `Bar` not found in `Cpp` [MemberNameNotFoundInInstScope]
+// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+4]]:13: note: in `Cpp` name lookup for `Bar` [InCppNameLookup]
 // CHECK:STDERR: fn MyF(bar: Cpp.Bar*);
 // CHECK:STDERR:             ^~~~~~~
 // CHECK:STDERR:
@@ -382,13 +376,13 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT:   name_binding_decl {
 // CHECK:STDOUT:     %bar.patt: %pattern_type = binding_pattern bar [concrete]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   %Cpp.ref.loc19_23: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
-// CHECK:STDOUT:   %Bar.ref.loc19_26: type = name_ref Bar, imports.%Bar.decl [concrete = constants.%Bar]
+// CHECK:STDOUT:   %Cpp.ref.loc16_23: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   %Bar.ref.loc16_26: type = name_ref Bar, imports.%Bar.decl [concrete = constants.%Bar]
 // CHECK:STDOUT:   %foo.ref: <error> = name_ref foo, <error> [concrete = <error>]
-// CHECK:STDOUT:   %.loc19: type = splice_block %ptr [concrete = constants.%ptr.f68] {
-// CHECK:STDOUT:     %Cpp.ref.loc19_12: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
-// CHECK:STDOUT:     %Bar.ref.loc19_15: type = name_ref Bar, imports.%Bar.decl [concrete = constants.%Bar]
-// CHECK:STDOUT:     %ptr: type = ptr_type %Bar.ref.loc19_15 [concrete = constants.%ptr.f68]
+// CHECK:STDOUT:   %.loc16: type = splice_block %ptr [concrete = constants.%ptr.f68] {
+// CHECK:STDOUT:     %Cpp.ref.loc16_12: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:     %Bar.ref.loc16_15: type = name_ref Bar, imports.%Bar.decl [concrete = constants.%Bar]
+// CHECK:STDOUT:     %ptr: type = ptr_type %Bar.ref.loc16_15 [concrete = constants.%ptr.f68]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %bar: %ptr.f68 = bind_name bar, <error> [concrete = <error>]
 // CHECK:STDOUT:   <elided>
@@ -532,7 +526,7 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT:
 // CHECK:STDOUT: imports {
 // CHECK:STDOUT:   %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
-// CHECK:STDOUT:     .Bar = <poisoned>
+// CHECK:STDOUT:     .Bar = <error>
 // CHECK:STDOUT:     import Cpp//...
 // CHECK:STDOUT:   }
 // CHECK:STDOUT: }
@@ -543,7 +537,7 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT:     %bar.param_patt: <error> = value_param_pattern %bar.patt, call_param0 [concrete]
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %bar.param: <error> = value_param call_param0
-// CHECK:STDOUT:     %.loc18: type = splice_block %ptr [concrete = <error>] {
+// CHECK:STDOUT:     %.loc15: type = splice_block %ptr [concrete = <error>] {
 // CHECK:STDOUT:       %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
 // CHECK:STDOUT:       %Bar.ref: <error> = name_ref Bar, <error> [concrete = <error>]
 // CHECK:STDOUT:       %ptr: type = ptr_type <error> [concrete = <error>]
diff --git a/toolchain/check/testdata/interop/cpp/class/union.carbon b/toolchain/check/testdata/interop/cpp/class/union.carbon
index 95c0affd6698..7d9fd327b8f5 100644
--- a/toolchain/check/testdata/interop/cpp/class/union.carbon
+++ b/toolchain/check/testdata/interop/cpp/class/union.carbon
@@ -121,18 +121,15 @@ union Bar {
 
 library "[[@TEST_NAME]]";
 
+// CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+4]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./static_data_member.h:4:24: error: semantics TODO: `Unsupported: Declaration type Var` [SemanticsTodo]
+// CHECK:STDERR:   static Bar* _Nonnull foo;
+// CHECK:STDERR:                        ^
 import Cpp library "static_data_member.h";
 
 fn MyF() {
   //@dump-sem-ir-begin
-  // CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+11]]:23: error: semantics TODO: `Unsupported: Declaration type Var` [SemanticsTodo]
-  // CHECK:STDERR:   let bar: Cpp.Bar* = Cpp.Bar.foo();
-  // CHECK:STDERR:                       ^~~~~~~~~~~
-  // CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+8]]:23: note: in `Cpp` name lookup for `foo` [InCppNameLookup]
-  // CHECK:STDERR:   let bar: Cpp.Bar* = Cpp.Bar.foo();
-  // CHECK:STDERR:                       ^~~~~~~~~~~
-  // CHECK:STDERR:
-  // CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+4]]:23: error: member name `foo` not found in `Cpp.Bar` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR: fail_todo_import_static_data_member.carbon:[[@LINE+4]]:23: note: in `Cpp` name lookup for `foo` [InCppNameLookup]
   // CHECK:STDERR:   let bar: Cpp.Bar* = Cpp.Bar.foo();
   // CHECK:STDERR:                       ^~~~~~~~~~~
   // CHECK:STDERR:
@@ -176,17 +173,14 @@ union Bar {};
 
 library "[[@TEST_NAME]]";
 
+// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+4]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./template.h:3:7: error: semantics TODO: `Unsupported: Declaration type ClassTemplate` [SemanticsTodo]
+// CHECK:STDERR: union Bar {};
+// CHECK:STDERR:       ^
 import Cpp library "template.h";
 
 //@dump-sem-ir-begin
-// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+11]]:13: error: semantics TODO: `Unsupported: Declaration type ClassTemplate` [SemanticsTodo]
-// CHECK:STDERR: fn MyF(bar: Cpp.Bar*);
-// CHECK:STDERR:             ^~~~~~~
-// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+8]]:13: note: in `Cpp` name lookup for `Bar` [InCppNameLookup]
-// CHECK:STDERR: fn MyF(bar: Cpp.Bar*);
-// CHECK:STDERR:             ^~~~~~~
-// CHECK:STDERR:
-// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+4]]:13: error: member name `Bar` not found in `Cpp` [MemberNameNotFoundInInstScope]
+// CHECK:STDERR: fail_todo_import_template.carbon:[[@LINE+4]]:13: note: in `Cpp` name lookup for `Bar` [InCppNameLookup]
 // CHECK:STDERR: fn MyF(bar: Cpp.Bar*);
 // CHECK:STDERR:             ^~~~~~~
 // CHECK:STDERR:
@@ -346,13 +340,13 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT:   name_binding_decl {
 // CHECK:STDOUT:     %bar.patt: %pattern_type = binding_pattern bar [concrete]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   %Cpp.ref.loc19_23: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
-// CHECK:STDOUT:   %Bar.ref.loc19_26: type = name_ref Bar, imports.%Bar.decl [concrete = constants.%Bar]
+// CHECK:STDOUT:   %Cpp.ref.loc16_23: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   %Bar.ref.loc16_26: type = name_ref Bar, imports.%Bar.decl [concrete = constants.%Bar]
 // CHECK:STDOUT:   %foo.ref: <error> = name_ref foo, <error> [concrete = <error>]
-// CHECK:STDOUT:   %.loc19: type = splice_block %ptr [concrete = constants.%ptr.f68] {
-// CHECK:STDOUT:     %Cpp.ref.loc19_12: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
-// CHECK:STDOUT:     %Bar.ref.loc19_15: type = name_ref Bar, imports.%Bar.decl [concrete = constants.%Bar]
-// CHECK:STDOUT:     %ptr: type = ptr_type %Bar.ref.loc19_15 [concrete = constants.%ptr.f68]
+// CHECK:STDOUT:   %.loc16: type = splice_block %ptr [concrete = constants.%ptr.f68] {
+// CHECK:STDOUT:     %Cpp.ref.loc16_12: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:     %Bar.ref.loc16_15: type = name_ref Bar, imports.%Bar.decl [concrete = constants.%Bar]
+// CHECK:STDOUT:     %ptr: type = ptr_type %Bar.ref.loc16_15 [concrete = constants.%ptr.f68]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %bar: %ptr.f68 = bind_name bar, <error> [concrete = <error>]
 // CHECK:STDOUT:   <elided>
@@ -420,7 +414,7 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT:
 // CHECK:STDOUT: imports {
 // CHECK:STDOUT:   %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
-// CHECK:STDOUT:     .Bar = <poisoned>
+// CHECK:STDOUT:     .Bar = <error>
 // CHECK:STDOUT:     import Cpp//...
 // CHECK:STDOUT:   }
 // CHECK:STDOUT: }
@@ -431,7 +425,7 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT:     %bar.param_patt: <error> = value_param_pattern %bar.patt, call_param0 [concrete]
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %bar.param: <error> = value_param call_param0
-// CHECK:STDOUT:     %.loc18: type = splice_block %ptr [concrete = <error>] {
+// CHECK:STDOUT:     %.loc15: type = splice_block %ptr [concrete = <error>] {
 // CHECK:STDOUT:       %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
 // CHECK:STDOUT:       %Bar.ref: <error> = name_ref Bar, <error> [concrete = <error>]
 // CHECK:STDOUT:       %ptr: type = ptr_type <error> [concrete = <error>]
diff --git a/toolchain/check/testdata/interop/cpp/function/pointer.carbon b/toolchain/check/testdata/interop/cpp/function/pointer.carbon
index 8a74192194b2..37f502dc01b5 100644
--- a/toolchain/check/testdata/interop/cpp/function/pointer.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/pointer.carbon
@@ -176,7 +176,7 @@ import Cpp library "nullable_pointer_param.h";
 fn F() {
   //@dump-sem-ir-begin
   var s: Cpp.S = {};
-  // CHECK:STDERR: fail_todo_import_nullable_pointer_param.carbon:[[@LINE+7]]:3: error: semantics TODO: `Unsupported: nullable pointer: S *` [SemanticsTodo]
+  // CHECK:STDERR: fail_todo_import_nullable_pointer_param.carbon:[[@LINE+7]]:3: error: semantics TODO: `Unsupported: parameter type: S *` [SemanticsTodo]
   // CHECK:STDERR:   Cpp.foo(&s);
   // CHECK:STDERR:   ^~~~~~~
   // CHECK:STDERR: fail_todo_import_nullable_pointer_param.carbon:[[@LINE+4]]:3: note: in `Cpp` name lookup for `foo` [InCppNameLookup]
@@ -524,8 +524,6 @@ fn F() {
 // CHECK:STDOUT:   %empty_struct_type: type = struct_type {} [concrete]
 // CHECK:STDOUT:   %pattern_type.7da: type = pattern_type %S [concrete]
 // CHECK:STDOUT:   %S.val: %S = struct_value () [concrete]
-// CHECK:STDOUT:   %foo.type: type = fn_type @foo [concrete]
-// CHECK:STDOUT:   %foo: %foo.type = struct_value () [concrete]
 // CHECK:STDOUT:   %ptr.5c7: type = ptr_type %S [concrete]
 // CHECK:STDOUT:   %T.as.Destroy.impl.Op.type.642: type = fn_type @T.as.Destroy.impl.Op, @T.as.Destroy.impl(%S) [concrete]
 // CHECK:STDOUT:   %T.as.Destroy.impl.Op.ab5: %T.as.Destroy.impl.Op.type.642 = struct_value () [concrete]
@@ -534,15 +532,10 @@ fn F() {
 // CHECK:STDOUT: imports {
 // CHECK:STDOUT:   %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
 // CHECK:STDOUT:     .S = %S.decl
-// CHECK:STDOUT:     .foo = %foo.decl
+// CHECK:STDOUT:     .foo = <error>
 // CHECK:STDOUT:     import Cpp//...
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %S.decl: type = class_decl @S [concrete = constants.%S] {} {}
-// CHECK:STDOUT:   %foo.decl: %foo.type = fn_decl @foo [concrete = constants.%foo] {
-// CHECK:STDOUT:     <elided>
-// CHECK:STDOUT:   } {
-// CHECK:STDOUT:     <elided>
-// CHECK:STDOUT:   }
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F() {
@@ -562,10 +555,9 @@ fn F() {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %s: ref %S = bind_name s, %s.var
 // CHECK:STDOUT:   %Cpp.ref.loc16: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
-// CHECK:STDOUT:   %foo.ref: %foo.type = name_ref foo, imports.%foo.decl [concrete = constants.%foo]
+// CHECK:STDOUT:   %foo.ref: <error> = name_ref foo, <error> [concrete = <error>]
 // CHECK:STDOUT:   %s.ref: ref %S = name_ref s, %s
 // CHECK:STDOUT:   %addr.loc16: %ptr.5c7 = addr_of %s.ref
-// CHECK:STDOUT:   %foo.call: init %empty_tuple.type = call %foo.ref(<error>)
 // CHECK:STDOUT:   %T.as.Destroy.impl.Op.bound: <bound method> = bound_method %s.var, constants.%T.as.Destroy.impl.Op.ab5
 // CHECK:STDOUT:   <elided>
 // CHECK:STDOUT:   %bound_method: <bound method> = bound_method %s.var, %T.as.Destroy.impl.Op.specific_fn
diff --git a/toolchain/check/testdata/interop/cpp/unsupported_decl_type.carbon b/toolchain/check/testdata/interop/cpp/unsupported_decl_type.carbon
index 1d33b673e323..f0eb4bdd1b1e 100644
--- a/toolchain/check/testdata/interop/cpp/unsupported_decl_type.carbon
+++ b/toolchain/check/testdata/interop/cpp/unsupported_decl_type.carbon
@@ -18,18 +18,15 @@ template<typename T> class C {};
 
 library "[[@TEST_NAME]]";
 
+// CHECK:STDERR: fail_todo_use_template.carbon:[[@LINE+4]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./template.h:2:28: error: semantics TODO: `Unsupported: Declaration type ClassTemplate` [SemanticsTodo]
+// CHECK:STDERR: template<typename T> class C {};
+// CHECK:STDERR:                            ^
 import Cpp library "template.h";
 
 fn F() {
   //@dump-sem-ir-begin
-  // CHECK:STDERR: fail_todo_use_template.carbon:[[@LINE+11]]:10: error: semantics TODO: `Unsupported: Declaration type ClassTemplate` [SemanticsTodo]
-  // CHECK:STDERR:   var c: Cpp.C({});
-  // CHECK:STDERR:          ^~~~~
-  // CHECK:STDERR: fail_todo_use_template.carbon:[[@LINE+8]]:10: note: in `Cpp` name lookup for `C` [InCppNameLookup]
-  // CHECK:STDERR:   var c: Cpp.C({});
-  // CHECK:STDERR:          ^~~~~
-  // CHECK:STDERR:
-  // CHECK:STDERR: fail_todo_use_template.carbon:[[@LINE+4]]:10: error: member name `C` not found in `Cpp` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR: fail_todo_use_template.carbon:[[@LINE+4]]:10: note: in `Cpp` name lookup for `C` [InCppNameLookup]
   // CHECK:STDERR:   var c: Cpp.C({});
   // CHECK:STDERR:          ^~~~~
   // CHECK:STDERR:
diff --git a/toolchain/lower/testdata/interop/cpp/fail_extern_c.carbon b/toolchain/lower/testdata/interop/cpp/fail_extern_c.carbon
index aae1b7678003..44d769110f04 100644
--- a/toolchain/lower/testdata/interop/cpp/fail_extern_c.carbon
+++ b/toolchain/lower/testdata/interop/cpp/fail_extern_c.carbon
@@ -26,17 +26,14 @@ extern "C" int foo;
 
 library "[[@TEST_NAME]]";
 
+// CHECK:STDERR: fail_todo_import_extern_c_variable.carbon:[[@LINE+4]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./extern_c_variable.h:2:16: error: semantics TODO: `Unsupported: Declaration type Var` [SemanticsTodo]
+// CHECK:STDERR: extern "C" int foo;
+// CHECK:STDERR:                ^
 import Cpp library "extern_c_variable.h";
 
 fn MyF() -> i32 {
-  // CHECK:STDERR: fail_todo_import_extern_c_variable.carbon:[[@LINE+11]]:10: error: semantics TODO: `Unsupported: Declaration type Var` [SemanticsTodo]
-  // CHECK:STDERR:   return Cpp.foo;
-  // CHECK:STDERR:          ^~~~~~~
-  // CHECK:STDERR: fail_todo_import_extern_c_variable.carbon:[[@LINE+8]]:10: note: in `Cpp` name lookup for `foo` [InCppNameLookup]
-  // CHECK:STDERR:   return Cpp.foo;
-  // CHECK:STDERR:          ^~~~~~~
-  // CHECK:STDERR:
-  // CHECK:STDERR: fail_todo_import_extern_c_variable.carbon:[[@LINE+4]]:10: error: member name `foo` not found in `Cpp` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR: fail_todo_import_extern_c_variable.carbon:[[@LINE+4]]:10: note: in `Cpp` name lookup for `foo` [InCppNameLookup]
   // CHECK:STDERR:   return Cpp.foo;
   // CHECK:STDERR:          ^~~~~~~
   // CHECK:STDERR: