diff --git a/toolchain/check/cpp/export.cpp b/toolchain/check/cpp/export.cpp
index 20cc8e51d00c..b7c959db6278 100644
--- a/toolchain/check/cpp/export.cpp
+++ b/toolchain/check/cpp/export.cpp
@@ -825,7 +825,10 @@ static auto BuildCppToCarbonThunkDecl(Context& context, SemIR::LocId loc_id,
             SemIR::Function::VirtualModifier::None &&
         target.function.virtual_modifier !=
             SemIR::Function::VirtualModifier::Override);
-    // TODO: Call setIsPureVirtual if VirtualModifier::Abstract is present.
+    if (target.function.virtual_modifier ==
+        SemIR::Function::VirtualModifier::Abstract) {
+      cast<clang::CXXMethodDecl>(thunk_function_decl)->setIsPureVirtual(true);
+    }
   } else {
     thunk_function_decl = clang::FunctionDecl::Create(
         ast_context, target.decl_context, clang_loc, name_info, thunk_qual_type,
diff --git a/toolchain/check/cpp/generate_ast.cpp b/toolchain/check/cpp/generate_ast.cpp
index 1573f8bf6693..cc3f65e23039 100644
--- a/toolchain/check/cpp/generate_ast.cpp
+++ b/toolchain/check/cpp/generate_ast.cpp
@@ -544,6 +544,11 @@ auto CarbonExternalASTSource::CompleteType(clang::TagDecl* tag_decl) -> void {
                method_decl,
                MakeVirtualFunctionSignature(*context_, method_decl)),
            .inst_id = function.first_decl_id()});
+      // An abstract function has no definition, so it doesn't need a thunk.
+      if (function.virtual_modifier ==
+          SemIR::Function::VirtualModifier::Abstract) {
+        continue;
+      }
       pending_virtual_functions.push_back(
           {.loc_id = SemIR::LocId(vtable_entry_id),
            .function_id = callee_function.function_id,
diff --git a/toolchain/check/testdata/interop/cpp/class/export/base.carbon b/toolchain/check/testdata/interop/cpp/class/export/base.carbon
index 7479f4225fde..191ae35cc954 100644
--- a/toolchain/check/testdata/interop/cpp/class/export/base.carbon
+++ b/toolchain/check/testdata/interop/cpp/class/export/base.carbon
@@ -145,6 +145,57 @@ class Derived : public Carbon::Abstract {
 };
 ''';
 
+// --- fail_variable_with_abstract_method.carbon
+library "[[@TEST_NAME]]";
+
+import Cpp;
+
+// TODO: We should support generating a base subobject destructor for an
+// abstract class, even though we refuse to generate a complete object
+// destructor.
+// CHECK:STDERR: fail_variable_with_abstract_method.carbon:[[@LINE+4]]:1: error: cannot access member of interface `Core.Destroy` in type `Abstract` that does not implement that interface [MissingImplInMemberAccess]
+// CHECK:STDERR: abstract class Abstract {
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+abstract class Abstract {
+  abstract fn F(self);
+}
+
+inline Cpp '''
+// CHECK:STDERR: fail_variable_with_abstract_method.carbon:[[@LINE+7]]:18: error: variable type 'Carbon::Abstract' is an abstract class [CppInteropParseError]
+// CHECK:STDERR:    24 | Carbon::Abstract x;
+// CHECK:STDERR:       |                  ^
+// CHECK:STDERR: fail_variable_with_abstract_method.carbon:[[@LINE-7]]:22: note: unimplemented pure virtual method 'F' in 'Abstract' [CppInteropParseNote]
+// CHECK:STDERR:    13 |   abstract fn F(self);
+// CHECK:STDERR:       |                      ^
+// CHECK:STDERR:
+Carbon::Abstract x;
+''';
+
+// --- fail_todo_abstract_method_overridden_in_cpp.carbon
+library "[[@TEST_NAME]]";
+
+import Cpp;
+
+// TODO: We should support generating a base subobject destructor for an
+// abstract class, even though we refuse to generate a complete object
+// destructor.
+// CHECK:STDERR: fail_todo_abstract_method_overridden_in_cpp.carbon:[[@LINE+4]]:1: error: cannot access member of interface `Core.Destroy` in type `Abstract` that does not implement that interface [MissingImplInMemberAccess]
+// CHECK:STDERR: abstract class Abstract {
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+abstract class Abstract {
+  abstract fn F(ref self);
+}
+
+// A C++ class that overrides the abstract method can be instantiated.
+inline Cpp '''
+struct Derived : Carbon::Abstract {
+  void F() & override {}
+};
+Derived d;
+''';
+
 // --- override_virtual_dtor.carbon
 library "[[@TEST_NAME]]";