diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index d03879e..21fe6e1 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -3114,9 +3114,10 @@
     
   assert(EvalResult.Val.isInt() && "Size expressions must be integers!");
   llvm::APSInt &Res = EvalResult.Val.getInt();
-
-  return Context.getConstantArrayType(VLATy->getElementType(),
-                                      Res, ArrayType::Normal, 0);
+  if (Res >= llvm::APSInt(Res.getBitWidth(), Res.isUnsigned()))
+    return Context.getConstantArrayType(VLATy->getElementType(),
+                                        Res, ArrayType::Normal, 0);
+  return QualType();
 }
 
 bool Sema::VerifyBitField(SourceLocation FieldLoc, IdentifierInfo *FieldName, 
diff --git a/test/Sema/struct-decl.c b/test/Sema/struct-decl.c
index cacd847..7d7961b 100644
--- a/test/Sema/struct-decl.c
+++ b/test/Sema/struct-decl.c
@@ -7,4 +7,5 @@
 
 struct foo {
 	char name[(int)&((struct bar *)0)->n];
+	char name2[(int)&((struct bar *)0)->n - 1]; //expected-error{{fields must have a constant size}}
 };