diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index ab5bd6b..6ec4d4a 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -2746,6 +2746,17 @@
           if (!lpointee->isVoidType())
             Diag(Loc, diag::ext_gnu_void_ptr)
               << lex->getSourceRange() << rex->getSourceRange();
+        } else if (rpointee->isFunctionType()) {
+          if (getLangOptions().CPlusPlus) {
+            Diag(Loc, diag::err_typecheck_pointer_arith_function_type)
+              << rex->getType() << rex->getSourceRange();
+            return QualType();
+          }
+          
+          // GNU extension: arithmetic on pointer to function
+          if (!lpointee->isFunctionType())
+            Diag(Loc, diag::ext_gnu_ptr_func_arith)
+              << lex->getType() << lex->getSourceRange();
         } else {
           Diag(Loc, diag::err_typecheck_sub_ptr_object)
             << rex->getType() << rex->getSourceRange();
diff --git a/test/Sema/pointer-subtract-compat.c b/test/Sema/pointer-subtract-compat.c
index 4ed6abf..9aebe9c 100644
--- a/test/Sema/pointer-subtract-compat.c
+++ b/test/Sema/pointer-subtract-compat.c
@@ -4,3 +4,8 @@
 int a(char* a, rchar* b) {
   return a-b;
 }
+
+// <rdar://problem/6520707> 
+void f0(void (*fp)(void)) {
+  int x = fp - fp; // expected-warning{{arithmetic on pointer to function type 'void (*)(void)' is a GNU extension}}
+}