1 files changed, 5 insertions, 2 deletions
diff --git a/AST/Type.cpp b/AST/Type.cpp
index 78e0dbbb27..e59569d2d6 100644
--- a/AST/Type.cpp
+++ b/AST/Type.cpp
@@ -444,8 +444,11 @@ bool Type::isArithmeticType() const {
   if (const BuiltinType *BT = dyn_cast<BuiltinType>(CanonicalType))
     return BT->getKind() != BuiltinType::Void;
   if (const TagType *TT = dyn_cast<TagType>(CanonicalType))
-    if (TT->getDecl()->getKind() == Decl::Enum)
-      return true;
+    if (const EnumDecl *ED = dyn_cast<EnumDecl>(TT->getDecl()))
+      // GCC allows forward declaration of enum types (forbid by C99 6.7.2.3p2).
+      // If a body isn't seen by the time we get here, we exclude it from
+      // being allowed in arithmetic expressions.
+      return ED->isDefinition();
   return isa<ComplexType>(CanonicalType) || isa<VectorType>(CanonicalType);
 }