2 files changed, 11 insertions, 1 deletions
diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
index 1d40d42c11d..bb4039e7f3a 100644
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -2736,7 +2736,7 @@ void CXXNameMangler::mangleType(const UnaryTransformType *T) {
     }
   }
 
-  mangleType(T->getUnderlyingType());
+  mangleType(T->getBaseType());
 }
 
 void CXXNameMangler::mangleType(const AutoType *T) {
diff --git a/clang/test/CodeGenCXX/mangle.cpp b/clang/test/CodeGenCXX/mangle.cpp
index 5012c3b3798..5d757102ed2 100644
--- a/clang/test/CodeGenCXX/mangle.cpp
+++ b/clang/test/CodeGenCXX/mangle.cpp
@@ -1101,3 +1101,13 @@ struct c {
   // CHECK-LABEL: @_ZN6test541cC2EPNS0_Ut0_E
 };
 }
+
+namespace test55 {
+enum E { R };
+
+template <typename T>
+void fn(T, __underlying_type(T)) {}
+
+template void fn<E>(E, __underlying_type(E));
+// CHECK-LABEL: @_ZN6test552fnINS_1EEEEvT_U3eutS2_
+}