diff --git a/include/swift/AST/DiagnosticsClangImporter.def b/include/swift/AST/DiagnosticsClangImporter.def
index ee7888c5f2e9f..b75b8a3c47b1f 100644
--- a/include/swift/AST/DiagnosticsClangImporter.def
+++ b/include/swift/AST/DiagnosticsClangImporter.def
@@ -257,6 +257,7 @@ NOTE(record_field_not_imported, none, "field %0 unavailable (cannot import)", (c
 NOTE(invoked_func_not_imported, none, "function %0 unavailable (cannot import)", (const clang::NamedDecl*))
 NOTE(record_method_not_imported, none, "method %0 unavailable (cannot import)", (const clang::NamedDecl*))
 NOTE(objc_property_not_imported, none, "property %0 unavailable (cannot import)", (const clang::NamedDecl*))
+NOTE(unsupported_return_type, none, "C++ function %0 is unavailable: return type is unavailable in Swift", (const clang::NamedDecl*))
 
 NOTE(placeholder_for_forward_declared_interface_member_access_failure, none,
      "class '%0' will be imported as an opaque placeholder class and may be "
diff --git a/lib/ClangImporter/ClangImporter.cpp b/lib/ClangImporter/ClangImporter.cpp
index 89789d64e7840..59e50a328f5ba 100644
--- a/lib/ClangImporter/ClangImporter.cpp
+++ b/lib/ClangImporter/ClangImporter.cpp
@@ -5622,13 +5622,7 @@ importName(const clang::NamedDecl *D,
 
 Type ClangImporter::importFunctionReturnType(
     const clang::FunctionDecl *clangDecl, DeclContext *dc) {
-  bool isInSystemModule =
-      cast<ClangModuleUnit>(dc->getModuleScopeContext())->isSystemModule();
-  bool allowNSUIntegerAsInt =
-      Impl.shouldAllowNSUIntegerAsInt(isInSystemModule, clangDecl);
-  if (auto imported =
-          Impl.importFunctionReturnType(dc, clangDecl, allowNSUIntegerAsInt)
-              .getType())
+  if (auto imported = Impl.importFunctionReturnType(clangDecl, dc).getType())
     return imported;
   return dc->getASTContext().getNeverType();
 }
diff --git a/lib/ClangImporter/ImportDecl.cpp b/lib/ClangImporter/ImportDecl.cpp
index cf15e538d4db5..0edc1076b2f69 100644
--- a/lib/ClangImporter/ImportDecl.cpp
+++ b/lib/ClangImporter/ImportDecl.cpp
@@ -3048,13 +3048,16 @@ namespace {
 
       if (auto recordType = dyn_cast<clang::RecordType>(
               decl->getReturnType().getCanonicalType())) {
-        Impl.addImportDiagnostic(
-            decl, Diagnostic(diag::reference_passed_by_value,
-                             Impl.SwiftContext.AllocateCopy(
-                                 recordType->getDecl()->getNameAsString()),
-                             "the return"),
-            decl->getLocation());
-        return recordHasReferenceSemantics(recordType->getDecl());
+        if (recordHasReferenceSemantics(recordType->getDecl())) {
+          Impl.addImportDiagnostic(
+              decl,
+              Diagnostic(diag::reference_passed_by_value,
+                         Impl.SwiftContext.AllocateCopy(
+                             recordType->getDecl()->getNameAsString()),
+                         "the return"),
+              decl->getLocation());
+          return true;
+        }
       }
 
       return false;
@@ -3391,6 +3394,14 @@ namespace {
         func->setAccess(AccessLevel::Public);
       }
 
+      if (!isa<clang::CXXConstructorDecl>(decl) && !importedType) {
+        if (!Impl.importFunctionReturnType(decl, result->getDeclContext())) {
+          Impl.addImportDiagnostic(
+              decl, Diagnostic(diag::unsupported_return_type, decl),
+              decl->getSourceRange().getBegin());
+          return nullptr;
+        }
+      }
       result->setIsObjC(false);
       result->setIsDynamic(false);
 
diff --git a/lib/ClangImporter/ImportType.cpp b/lib/ClangImporter/ImportType.cpp
index 2fd3508e4e9fd..3c355c8b2c4ed 100644
--- a/lib/ClangImporter/ImportType.cpp
+++ b/lib/ClangImporter/ImportType.cpp
@@ -2074,6 +2074,15 @@ applyImportTypeAttrs(ImportTypeAttrs attrs, Type type,
   return type;
 }
 
+ImportedType ClangImporter::Implementation::importFunctionReturnType(
+    const clang::FunctionDecl *clangDecl, DeclContext *dc) {
+  bool isInSystemModule =
+      cast<ClangModuleUnit>(dc->getModuleScopeContext())->isSystemModule();
+  bool allowNSUIntegerAsInt =
+      shouldAllowNSUIntegerAsInt(isInSystemModule, clangDecl);
+  return importFunctionReturnType(dc, clangDecl, allowNSUIntegerAsInt);
+}
+
 ImportedType ClangImporter::Implementation::importFunctionReturnType(
     DeclContext *dc, const clang::FunctionDecl *clangDecl,
     bool allowNSUIntegerAsInt) {
diff --git a/lib/ClangImporter/ImporterImpl.h b/lib/ClangImporter/ImporterImpl.h
index 27aef3e217a22..7cf17144a3853 100644
--- a/lib/ClangImporter/ImporterImpl.h
+++ b/lib/ClangImporter/ImporterImpl.h
@@ -1340,6 +1340,9 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
                                         const clang::FunctionDecl *clangDecl,
                                         bool allowNSUIntegerAsInt);
 
+  ImportedType importFunctionReturnType(const clang::FunctionDecl *clangDecl,
+                                        DeclContext *dc);
+
   /// Import the parameter list for a function
   ///
   /// \param clangDecl The underlying declaration, if any; should only be
diff --git a/test/Interop/Cxx/class/returns-unavailable-class.swift b/test/Interop/Cxx/class/returns-unavailable-class.swift
new file mode 100644
index 0000000000000..7e448d1d0f9fd
--- /dev/null
+++ b/test/Interop/Cxx/class/returns-unavailable-class.swift
@@ -0,0 +1,65 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: %target-swift-ide-test -print-module -module-to-print=CxxModule -I %t/Inputs -source-filename=x -enable-experimental-cxx-interop | %FileCheck %s
+
+// RUN: %target-swift-frontend -typecheck -verify -I %t/Inputs -enable-experimental-cxx-interop %t/test.swift
+
+// RUN: not %target-swift-frontend -typecheck -I %t/Inputs -enable-experimental-cxx-interop %t/test.swift 2>&1 | %FileCheck --check-prefix=NOTE %s
+
+
+//--- Inputs/module.modulemap
+module CxxTypes {
+    header "types.h"
+    requires cplusplus
+}
+
+module CxxModule {
+    header "header.h"
+    requires cplusplus
+}
+
+//--- Inputs/types.h
+
+template<class T>
+class TemplateInTypesModule {
+public:
+    T x, y;
+};
+
+//--- Inputs/header.h
+
+#pragma clang module import CxxTypes
+
+class Struct {
+public:
+    int x, y;
+
+    TemplateInTypesModule<int> returnsClassInTypesModules() const;
+
+    void takesClassInTypesModules(TemplateInTypesModule<int>) const;
+    void takesClassInTypesModulesRef(const TemplateInTypesModule<int> &) const;
+};
+
+// CHECK: struct Struct {
+// CHECK-NEXT:   init()
+// CHECK-NEXT:   init(x: Int32, y: Int32)
+// CHECK-NEXT:   var x: Int32
+// CHECK-NEXT:   var y: Int32
+// CHECK-NEXT: }
+
+// CHECK-NOT: funcWithClass
+
+TemplateInTypesModule<int> funcWithClassInTypesModules();
+void funcWithClassInTypesModulesParam(TemplateInTypesModule<int>);
+void funcWithClassInTypesModulesParamRef(const TemplateInTypesModule<int> &);
+
+//--- test.swift
+
+import CxxModule
+
+func test() {
+    funcWithClassInTypesModules() // expected-error {{cannot find 'funcWithClassInTypesModules' in scope}}
+    Struct().returnsClassInTypesModules() // expected-error {{value of type 'Struct' has no member 'returnsClassInTypesModules'}}
+}
+
+// NOTE: note: C++ function 'funcWithClassInTypesModules' is unavailable: return type is unavailable in Swift