diff --git a/lib/SymbolGraphGen/SymbolGraphASTWalker.cpp b/lib/SymbolGraphGen/SymbolGraphASTWalker.cpp
index 7e74539228496..d4b4a2c6969fc 100644
--- a/lib/SymbolGraphGen/SymbolGraphASTWalker.cpp
+++ b/lib/SymbolGraphGen/SymbolGraphASTWalker.cpp
@@ -21,6 +21,20 @@
 using namespace swift;
 using namespace symbolgraphgen;
 
+namespace {
+
+/// Compare the two \c ModuleDecl instances to see whether they are the same.
+///
+/// Pass \c true to the \c ignoreUnderlying argument to consider two modules the same even if
+/// one is a Swift module and the other a non-Swift module. This allows a Swift module and its
+/// underlying Clang module to compare as equal.
+bool areModulesEqual(const ModuleDecl *lhs, const ModuleDecl *rhs, bool ignoreUnderlying = false) {
+  return lhs->getNameStr() == rhs->getNameStr()
+    && (ignoreUnderlying || lhs->isNonSwiftModule() == rhs->isNonSwiftModule());
+}
+
+} // anonymous namespace
+
 SymbolGraphASTWalker::SymbolGraphASTWalker(ModuleDecl &M,
                                            const SmallPtrSet<ModuleDecl *, 4> ExportedImportedModules,
                                            const SymbolGraphOptions &Options)
@@ -45,10 +59,10 @@ SymbolGraph *SymbolGraphASTWalker::getModuleSymbolGraph(const Decl *D) {
     }
   }
 
-  if (this->M.getNameStr().equals(M->getNameStr())) {
+  if (areModulesEqual(&this->M, M, true)) {
     return &MainGraph;
   } else if (MainGraph.DeclaringModule.hasValue() &&
-      MainGraph.DeclaringModule.getValue()->getNameStr().equals(M->getNameStr())) {
+             areModulesEqual(MainGraph.DeclaringModule.getValue(), M, true)) {
     // Cross-import overlay modules already appear as "extensions" of their declaring module; we
     // should put actual extensions of that module into the main graph
     return &MainGraph;
@@ -220,6 +234,6 @@ bool SymbolGraphASTWalker::isFromExportedImportedModule(const Decl* D) const {
     auto *M = D->getModuleContext();
     
     return llvm::any_of(ExportedImportedModules, [&M](const auto *MD) {
-        return M->getNameStr().equals(MD->getModuleContext()->getNameStr());
+        return areModulesEqual(M, MD->getModuleContext());
     });
 }
diff --git a/test/SymbolGraph/ClangImporter/ForeignExtensions.swift b/test/SymbolGraph/ClangImporter/ForeignExtensions.swift
new file mode 100644
index 0000000000000..ee0cd45a0170f
--- /dev/null
+++ b/test/SymbolGraph/ClangImporter/ForeignExtensions.swift
@@ -0,0 +1,23 @@
+// RUN: %empty-directory(%t)
+// RUN: cp -r %S/Inputs/EmitWhileBuilding/EmitWhileBuilding.framework %t
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -enable-objc-interop -emit-module-path %t/EmitWhileBuilding.framework/Modules/EmitWhileBuilding.swiftmodule/%target-swiftmodule-name -import-underlying-module -F %t -module-name EmitWhileBuilding -disable-objc-attr-requires-foundation-module %s %S/Inputs/EmitWhileBuilding/Extra.swift -emit-symbol-graph -emit-symbol-graph-dir %t
+// RUN: %FileCheck %s --input-file %t/EmitWhileBuilding.symbols.json --check-prefix BASE
+// RUN: %FileCheck %s --input-file %t/EmitWhileBuilding@Swift.symbols.json --check-prefix EXTENSION
+
+// RUN: %target-swift-symbolgraph-extract -sdk %clang-importer-sdk -module-name EmitWhileBuilding -F %t -output-dir %t -pretty-print -v
+// RUN: %FileCheck %s --input-file %t/EmitWhileBuilding.symbols.json --check-prefix BASE
+// RUN: %FileCheck %s --input-file %t/EmitWhileBuilding@Swift.symbols.json --check-prefix EXTENSION
+
+// REQUIRES: objc_interop
+
+// ensure that the symbol `String.Foo.bar` does not appear in the base module's symbol graph
+
+// BASE-NOT:     "s:SS17EmitWhileBuildingE3FooO3baryA2CmF",
+// EXTENSION:    "s:SS17EmitWhileBuildingE3FooO3baryA2CmF",
+
+public extension String {
+    enum Foo {
+        case bar
+    }
+}
+