Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -3008,6 +3008,10 @@
 
 static void handleTransparentUnionAttr(Sema &S, Decl *D,
                                        const AttributeList &Attr) {
+  if (S.getLangOpts().CPlusPlus) {
+    return;
+  }
+
   // Try to find the underlying union declaration.
   RecordDecl *RD = nullptr;
   TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(D);
Index: test/SemaCXX/attr-gnu.cpp
===================================================================
--- test/SemaCXX/attr-gnu.cpp
+++ test/SemaCXX/attr-gnu.cpp
@@ -27,3 +27,19 @@
   void test3() __attribute__((cf_unknown_transfer)) override {} // Ok, not known to GCC.
 };
 }
+
+template<typename T>
+union Tu { T b; } __attribute__((transparent_union));
+
+template<typename T>
+union Tu2 { int x; T b; } __attribute__((transparent_union));
+
+union Tu3 { int x; } __attribute((transparent_union));
+
+void tuTest1(Tu<int> u); // expected-note {{candidate function not viable: no known conversion from 'int' to 'Tu<int>' for 1st argument}}
+void tuTest2(Tu3 u); // expected-note {{candidate function not viable: no known conversion from 'int' to 'Tu3' for 1st argument}}
+void tu() {
+  int x = 2;
+  tuTest1(x); // expected-error {{no matching function for call to 'tuTest1'}}
+  tuTest2(x); // expected-error {{no matching function for call to 'tuTest2'}}
+}