diff --git a/clang/unittests/AST/ASTImporterTest.cpp b/clang/unittests/AST/ASTImporterTest.cpp
index 6b8315f..8b2f7c5 100644
--- a/clang/unittests/AST/ASTImporterTest.cpp
+++ b/clang/unittests/AST/ASTImporterTest.cpp
@@ -5122,6 +5122,51 @@
   EXPECT_EQ(ToLSize, FromLSize);
 }
 
+struct LLDBLookupTest : ASTImporterOptionSpecificTestBase {
+  LLDBLookupTest() {
+    Creator = [](ASTContext &ToContext, FileManager &ToFileManager,
+                 ASTContext &FromContext, FileManager &FromFileManager,
+                 bool MinimalImport,
+                 const std::shared_ptr<ASTImporterSharedState> &SharedState) {
+      return new ASTImporter(ToContext, ToFileManager, FromContext,
+                             FromFileManager, MinimalImport,
+                             // We use the regular lookup.
+                             /*SharedState=*/nullptr);
+    };
+  }
+};
+
+TEST_P(LLDBLookupTest, ImporterShouldFindInTransparentContext) {
+  TranslationUnitDecl *ToTU = getToTuDecl(
+      R"(
+      extern "C" {
+        class X{};
+      };
+      )",
+      Lang_CXX);
+  auto *ToX = FirstDeclMatcher<CXXRecordDecl>().match(
+      ToTU, cxxRecordDecl(hasName("X")));
+
+  // Set up a stub external storage.
+  ToTU->setHasExternalLexicalStorage(true);
+  // Set up DeclContextBits.HasLazyExternalLexicalLookups to true.
+  ToTU->setMustBuildLookupTable();
+  struct TestExternalASTSource : ExternalASTSource {};
+  ToTU->getASTContext().setExternalSource(new TestExternalASTSource());
+
+  Decl *FromTU = getTuDecl(
+      R"(
+        class X;
+      )",
+      Lang_CXX);
+  auto *FromX = FirstDeclMatcher<CXXRecordDecl>().match(
+      FromTU, cxxRecordDecl(hasName("X")));
+  auto *ImportedX = Import(FromX, Lang_CXX);
+  // The lookup must find the existing class definition in the LinkageSpecDecl.
+  // Then the importer renders the existing and the new decl into one chain.
+  EXPECT_EQ(ImportedX->getCanonicalDecl(), ToX->getCanonicalDecl());
+}
+
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, ASTImporterLookupTableTest,
                         DefaultTestValuesForRunOptions, );
 
@@ -5168,5 +5213,8 @@
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportVariables,
                         DefaultTestValuesForRunOptions, );
 
+INSTANTIATE_TEST_CASE_P(ParameterizedTests, LLDBLookupTest,
+                        DefaultTestValuesForRunOptions, );
+
 } // end namespace ast_matchers
 } // end namespace clang