diff --git a/toolchain/check/convert.cpp b/toolchain/check/convert.cpp
index 4c4f0e90bc33..8b5b265d14d8 100644
--- a/toolchain/check/convert.cpp
+++ b/toolchain/check/convert.cpp
@@ -975,8 +975,7 @@ auto Convert(Context& context, SemIR::LocId loc_id, SemIR::InstId expr_id,
   }
 
   // If this is not a builtin conversion, try an `ImplicitAs` conversion.
-  SemIR::Inst expr = sem_ir.insts().Get(expr_id);
-  if (expr.type_id() != target.type_id) {
+  if (sem_ir.insts().Get(expr_id).type_id() != target.type_id) {
     SemIR::InstId interface_args[] = {
         context.types().GetInstId(target.type_id)};
     Operator op = {
@@ -1019,7 +1018,8 @@ auto Convert(Context& context, SemIR::LocId loc_id, SemIR::InstId expr_id,
   switch (SemIR::GetExprCategory(sem_ir, expr_id)) {
     case SemIR::ExprCategory::NotExpr:
     case SemIR::ExprCategory::Mixed:
-      CARBON_FATAL("Unexpected expression {0} after builtin conversions", expr);
+      CARBON_FATAL("Unexpected expression {0} after builtin conversions",
+                   sem_ir.insts().Get(expr_id));
 
     case SemIR::ExprCategory::Error:
       return SemIR::InstId::BuiltinError;
@@ -1057,7 +1057,7 @@ auto Convert(Context& context, SemIR::LocId loc_id, SemIR::InstId expr_id,
       // TODO: Support types with custom value representations.
       expr_id = context.AddInst<SemIR::BindValue>(
           context.insts().GetLocId(expr_id),
-          {.type_id = expr.type_id(), .value_id = expr_id});
+          {.type_id = target.type_id, .value_id = expr_id});
       // We now have a value expression.
       [[fallthrough]];
 
diff --git a/toolchain/check/testdata/operators/overloaded/implicit_as.carbon b/toolchain/check/testdata/operators/overloaded/implicit_as.carbon
index bf116f85f13d..9995aefe5b5a 100644
--- a/toolchain/check/testdata/operators/overloaded/implicit_as.carbon
+++ b/toolchain/check/testdata/operators/overloaded/implicit_as.carbon
@@ -313,7 +313,7 @@ fn Test() {
 // CHECK:STDOUT:   %.loc30_18.7: init i32 = converted %Source.call.loc30, %Convert.call.loc30
 // CHECK:STDOUT:   %.loc30_18.8: ref i32 = temporary_storage
 // CHECK:STDOUT:   %.loc30_18.9: ref i32 = temporary %.loc30_18.8, %.loc30_18.7
-// CHECK:STDOUT:   %.loc30_18.10: %X = bind_value %.loc30_18.9
+// CHECK:STDOUT:   %.loc30_18.10: i32 = bind_value %.loc30_18.9
 // CHECK:STDOUT:   %Sink_i32.call: init %.1 = call %Sink_i32.ref(%.loc30_18.10)
 // CHECK:STDOUT:   %Sink_X.ref: %Sink_X.type = name_ref Sink_X, file.%Sink_X.decl [template = constants.%Sink_X]
 // CHECK:STDOUT:   %Source.ref.loc31: %Source.type = name_ref Source, file.%Source.decl [template = constants.%Source]
@@ -334,7 +334,7 @@ fn Test() {
 // CHECK:STDOUT:   %Convert.call.loc31: init %X = call %.loc31_16.7(%.loc31_16.9) to %.loc31_16.8
 // CHECK:STDOUT:   %.loc31_16.10: init %X = converted %Source.call.loc31, %Convert.call.loc31
 // CHECK:STDOUT:   %.loc31_16.11: ref %X = temporary %.loc31_16.8, %.loc31_16.10
-// CHECK:STDOUT:   %.loc31_16.12: i32 = bind_value %.loc31_16.11
+// CHECK:STDOUT:   %.loc31_16.12: %X = bind_value %.loc31_16.11
 // CHECK:STDOUT:   %Sink_X.call: init %.1 = call %Sink_X.ref(%.loc31_16.12)
 // CHECK:STDOUT:   return
 // CHECK:STDOUT: }
diff --git a/toolchain/lower/constant.cpp b/toolchain/lower/constant.cpp
index 0d93f8aab91c..1f6021fbf10e 100644
--- a/toolchain/lower/constant.cpp
+++ b/toolchain/lower/constant.cpp
@@ -260,6 +260,12 @@ auto LowerConstants(FileContext& file_context,
     }
 
     auto inst = file_context.sem_ir().insts().Get(inst_id);
+    if (inst.type_id().is_valid() &&
+        !file_context.sem_ir().types().IsComplete(inst.type_id())) {
+      // If a constant doesn't have a complete type, that means we imported it
+      // but didn't actually use it.
+      continue;
+    }
     llvm::Constant* value = nullptr;
     CARBON_KIND_SWITCH(inst) {
 #define CARBON_SEM_IR_INST_KIND(Name)            \
diff --git a/toolchain/lower/file_context.h b/toolchain/lower/file_context.h
index 0c087d8f7337..c2f1d5772249 100644
--- a/toolchain/lower/file_context.h
+++ b/toolchain/lower/file_context.h
@@ -55,7 +55,8 @@ class FileContext {
   auto GetType(SemIR::TypeId type_id) -> llvm::Type* {
     // InvalidType should not be passed in.
     CARBON_CHECK(type_id.index >= 0, "{0}", type_id);
-    CARBON_CHECK(types_[type_id.index], "Missing type {0}", type_id);
+    CARBON_CHECK(types_[type_id.index], "Missing type {0}: {1}", type_id,
+                 sem_ir().types().GetAsInst(type_id));
     return types_[type_id.index];
   }
 
diff --git a/toolchain/lower/testdata/class/convert.carbon b/toolchain/lower/testdata/class/convert.carbon
new file mode 100644
index 000000000000..4c9fab477eb7
--- /dev/null
+++ b/toolchain/lower/testdata/class/convert.carbon
@@ -0,0 +1,81 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/class/convert.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/class/convert.carbon
+
+class IntWrapper {
+  var n: i32;
+}
+
+impl IntWrapper as Core.ImplicitAs(i32) {
+  fn Convert[self: Self]() -> i32 { return self.n; }
+}
+
+fn Consume(n: i32) {}
+
+fn DoIt() {
+  var w: IntWrapper = {.n = 42};
+  Consume(w);
+}
+
+// CHECK:STDOUT: ; ModuleID = 'convert.carbon'
+// CHECK:STDOUT: source_filename = "convert.carbon"
+// CHECK:STDOUT:
+// CHECK:STDOUT: @struct.loc22_32 = internal constant { i32 } { i32 42 }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i32 @"_CConvert.IntWrapper.Main:ImplicitAs.Core"(ptr %self) !dbg !4 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %.loc16_48.1.n = getelementptr inbounds nuw { i32 }, ptr %self, i32 0, i32 0, !dbg !7
+// CHECK:STDOUT:   %.loc16_48.2 = load i32, ptr %.loc16_48.1.n, align 4, !dbg !7
+// CHECK:STDOUT:   ret i32 %.loc16_48.2, !dbg !8
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define void @_CConsume.Main(i32 %n) !dbg !9 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !10
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define void @_CDoIt.Main() !dbg !11 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %w.var = alloca { i32 }, align 8, !dbg !12
+// CHECK:STDOUT:   %.loc22_31.2.n = getelementptr inbounds nuw { i32 }, ptr %w.var, i32 0, i32 0, !dbg !13
+// CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %w.var, ptr align 4 @struct.loc22_32, i64 4, i1 false), !dbg !14
+// CHECK:STDOUT:   %Convert.call = call i32 @"_CConvert.IntWrapper.Main:ImplicitAs.Core"(ptr %w.var), !dbg !15
+// CHECK:STDOUT:   %.loc23_11.6.temp = alloca i32, align 4, !dbg !15
+// CHECK:STDOUT:   store i32 %Convert.call, ptr %.loc23_11.6.temp, align 4, !dbg !15
+// CHECK:STDOUT:   %.loc23_11.8 = load i32, ptr %.loc23_11.6.temp, align 4, !dbg !15
+// CHECK:STDOUT:   call void @_CConsume.Main(i32 %.loc23_11.8), !dbg !16
+// CHECK:STDOUT:   ret void, !dbg !17
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nocallback nofree nounwind willreturn memory(argmem: readwrite)
+// CHECK:STDOUT: declare void @llvm.memcpy.p0.p0.i64(ptr noalias nocapture writeonly, ptr noalias nocapture readonly, i64, i1 immarg) #0
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nocallback nofree nounwind willreturn memory(argmem: readwrite) }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.module.flags = !{!0, !1}
+// CHECK:STDOUT: !llvm.dbg.cu = !{!2}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !2 = distinct !DICompileUnit(language: DW_LANG_C, file: !3, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !3 = !DIFile(filename: "convert.carbon", directory: "")
+// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "Convert", linkageName: "_CConvert.IntWrapper.Main:ImplicitAs.Core", scope: null, file: !3, line: 16, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !5 = !DISubroutineType(types: !6)
+// CHECK:STDOUT: !6 = !{}
+// CHECK:STDOUT: !7 = !DILocation(line: 16, column: 44, scope: !4)
+// CHECK:STDOUT: !8 = !DILocation(line: 16, column: 37, scope: !4)
+// CHECK:STDOUT: !9 = distinct !DISubprogram(name: "Consume", linkageName: "_CConsume.Main", scope: null, file: !3, line: 19, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !10 = !DILocation(line: 19, column: 1, scope: !9)
+// CHECK:STDOUT: !11 = distinct !DISubprogram(name: "DoIt", linkageName: "_CDoIt.Main", scope: null, file: !3, line: 21, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !12 = !DILocation(line: 22, column: 7, scope: !11)
+// CHECK:STDOUT: !13 = !DILocation(line: 22, column: 23, scope: !11)
+// CHECK:STDOUT: !14 = !DILocation(line: 22, column: 3, scope: !11)
+// CHECK:STDOUT: !15 = !DILocation(line: 23, column: 11, scope: !11)
+// CHECK:STDOUT: !16 = !DILocation(line: 23, column: 3, scope: !11)
+// CHECK:STDOUT: !17 = !DILocation(line: 21, column: 1, scope: !11)