Index: lib/AST/ItaniumMangle.cpp
===================================================================
--- lib/AST/ItaniumMangle.cpp
+++ lib/AST/ItaniumMangle.cpp
@@ -69,6 +69,14 @@
   if (const CapturedDecl *CD = dyn_cast<CapturedDecl>(DC))
     return getEffectiveDeclContext(CD);
 
+  if (const auto *VD = dyn_cast<VarDecl>(D))
+    if (VD->isExternC())
+      return VD->getASTContext().getTranslationUnitDecl();
+
+  if (const auto *FD = dyn_cast<FunctionDecl>(D))
+    if (FD->isExternC())
+      return FD->getASTContext().getTranslationUnitDecl();
+
   return DC;
 }
 
Index: test/CodeGenCXX/mangle-template.cpp
===================================================================
--- test/CodeGenCXX/mangle-template.cpp
+++ test/CodeGenCXX/mangle-template.cpp
@@ -28,8 +28,7 @@
 // CHECK: void @test3_f0
 extern "C" void test3_f0(float) {}
 template<void (&)(float)> struct t1 {};
-// FIXME: Fails because we tack on a namespace.
-// CHECK-FIXME: void @_ZN5test32f1ENS_2t1ILZ8test3_f0EEE(
+// CHECK: void @_ZN5test32f1ENS_2t1IL_Z8test3_f0EEE(
 void f1(t1<test3_f0> a0) {}
 }
 
@@ -37,7 +36,7 @@
 // CHECK: void @test4_f0
 extern "C" void test4_f0(float) {}
 template<void (*)(float)> struct t1 {};
-// CHECK: void @_ZN5test42f1ENS_2t1IXadL_ZNS_8test4_f0EEEEE(
+// CHECK: void @_ZN5test42f1ENS_2t1IXadL_Z8test4_f0EEEE(
 void f1(t1<test4_f0> a0) {}
 }