Index: Sema/SemaExpr.cpp
===================================================================
--- Sema/SemaExpr.cpp	(revision 46872)
+++ Sema/SemaExpr.cpp	(working copy)
@@ -1329,10 +1343,40 @@
   if (lex->getType()->isArithmeticType() && rex->getType()->isArithmeticType())
     return compType;
 
-  if (lex->getType()->isPointerType() && rex->getType()->isIntegerType())
-    return lex->getType();
-  if (lex->getType()->isIntegerType() && rex->getType()->isPointerType())
-    return rex->getType();
+  if (const PointerType* PTy = lex->getType()->getAsPointerType()) {
+    if (rex->getType()->isIntegerType()) {
+      // Check for arithmetic on pointers to incomplete types
+      if (!PTy->getPointeeType()->isObjectType()) {
+        if (PTy->getPointeeType()->isVoidType()) {
+          Diag(loc, diag::ext_gnu_void_ptr, 
+               lex->getSourceRange(), rex->getSourceRange());
+        } else {
+          Diag(loc, diag::err_typecheck_arithmetic_incomplete_type,
+               lex->getType().getAsString(), lex->getSourceRange());
+          return QualType();
+        }
+      }
+      return lex->getType();
+    }
+  }
+
+  if (const PointerType* PTy = rex->getType()->getAsPointerType()) {
+    if (lex->getType()->isIntegerType()) {
+      // Check for arithmetic on pointers to incomplete types
+      if (!PTy->getPointeeType()->isObjectType()) {
+        if (PTy->getPointeeType()->isVoidType()) {
+          Diag(loc, diag::ext_gnu_void_ptr, 
+               rex->getSourceRange(), lex->getSourceRange());
+        } else {
+          Diag(loc, diag::err_typecheck_arithmetic_incomplete_type,
+               rex->getType().getAsString(), rex->getSourceRange());
+          return QualType();
+        }
+      }
+      return rex->getType();
+    }
+  }
+
   return InvalidOperands(loc, lex, rex);
 }