Index: cfe/trunk/lib/AST/ItaniumMangle.cpp
===================================================================
--- cfe/trunk/lib/AST/ItaniumMangle.cpp
+++ cfe/trunk/lib/AST/ItaniumMangle.cpp
@@ -4273,8 +4273,11 @@
   }
 
   case Expr::GNUNullExprClass:
-    // FIXME: should this really be mangled the same as nullptr?
-    // fallthrough
+    // Mangle as if an integer literal 0.
+    Out << 'L';
+    mangleType(E->getType());
+    Out << "0E";
+    break;
 
   case Expr::CXXNullPtrLiteralExprClass: {
     Out << "LDnE";
Index: cfe/trunk/test/CodeGenCXX/mangle-exprs.cpp
===================================================================
--- cfe/trunk/test/CodeGenCXX/mangle-exprs.cpp
+++ cfe/trunk/test/CodeGenCXX/mangle-exprs.cpp
@@ -373,3 +373,19 @@
   template<typename T> void f(decltype(T{.a.b[3][1 ... 4] = 9}) x) {}
   void use_f(A a) { f<A>(a); }
 }
+
+namespace null {
+  template <decltype(nullptr) P>
+  void cpp_nullptr(typename enable_if<P == nullptr>::type* = 0) {
+  }
+
+  template <void *P>
+  void gnu_null(typename enable_if<P == __null>::type* = 0) {
+  }
+
+  // CHECK-LABEL: define {{.*}} @_ZN4null11cpp_nullptrILDn0EEEvPN9enable_ifIXeqT_LDnEEvE4typeE
+  template void cpp_nullptr<nullptr>(void *);
+
+  // CHECK-LABEL: define {{.*}} @_ZN4null8gnu_nullILPv0EEEvPN9enable_ifIXeqT_Ll0EEvE4typeE
+  template void gnu_null<nullptr>(void *);
+}