diff --git a/AST/ASTContext.cpp b/AST/ASTContext.cpp
index d01de2b..d4a689c 100644
--- a/AST/ASTContext.cpp
+++ b/AST/ASTContext.cpp
@@ -1555,22 +1555,14 @@
 // C99 6.2.7p1: If both are complete types, then the following additional
 // requirements apply...FIXME (handle compatibility across source files).
 bool ASTContext::tagTypesAreCompatible(QualType lhs, QualType rhs) {
-  TagDecl *ldecl = cast<TagType>(lhs.getCanonicalType())->getDecl();
-  TagDecl *rdecl = cast<TagType>(rhs.getCanonicalType())->getDecl();
-  
-  if (ldecl->getKind() == Decl::Struct && rdecl->getKind() == Decl::Struct) {
-    if (ldecl->getIdentifier() == rdecl->getIdentifier())
-      return true;
-  }
-  if (ldecl->getKind() == Decl::Union && rdecl->getKind() == Decl::Union) {
-    if (ldecl->getIdentifier() == rdecl->getIdentifier())
-      return true;
-  }
   // "Class" and "id" are compatible built-in structure types.
   if (isObjCIdType(lhs) && isObjCClassType(rhs) ||
       isObjCClassType(lhs) && isObjCIdType(rhs))
     return true;
-  return false;
+
+  // Within a translation unit a tag type is
+  // only compatible with itself.
+  return lhs.getCanonicalType() == rhs.getCanonicalType();
 }
 
 bool ASTContext::pointerTypesAreCompatible(QualType lhs, QualType rhs) {
diff --git a/test/Sema/struct-compat.c b/test/Sema/struct-compat.c
new file mode 100644
index 0000000..d63f9cd
--- /dev/null
+++ b/test/Sema/struct-compat.c
@@ -0,0 +1,19 @@
+/* RUN: clang %s -fsyntax-only -pedantic -verify
+ */
+
+extern struct {int a;} x; // expected-error{{previous definition is here}}
+extern struct {int a;} x; // expected-error{{redefinition of 'x'}}
+
+struct x;
+int a(struct x* b) {
+// FIXME: This test currently fails
+// Per C99 6.7.2.3, since the outer and inner "struct x"es have different
+// scopes, they don't refer to the same type, and are therefore incompatible
+struct x {int a;} *c = b;
+}
+
+struct x {int a;} r;
+int b() {
+// FIXME: This test currently also fails
+struct x {char x;} s = r;
+}