diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index cb947fa..c459192 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1714,6 +1714,8 @@
 def warn_missing_type_specifier : Warning<
   "type specifier missing, defaults to 'int'">,
   InGroup<ImplicitInt>;
+def err_decimal_unsupported : Error<
+  "GNU decimal type extension not supported">;
 def err_missing_type_specifier : Error<
   "C++ requires a type specifier for all declarations">;
 def err_missing_param_declspec : Error<
diff --git a/lib/Sema/SemaType.cpp b/lib/Sema/SemaType.cpp
index d04a5ad..972ac82 100644
--- a/lib/Sema/SemaType.cpp
+++ b/lib/Sema/SemaType.cpp
@@ -164,7 +164,10 @@
   case DeclSpec::TST_decimal32:    // _Decimal32
   case DeclSpec::TST_decimal64:    // _Decimal64
   case DeclSpec::TST_decimal128:   // _Decimal128
-    assert(0 && "FIXME: GNU decimal extensions not supported yet!"); 
+    Diag(DS.getTypeSpecTypeLoc(), diag::err_decimal_unsupported);
+    Result = Context.IntTy;
+    isInvalid = true;
+    break;
   case DeclSpec::TST_class:
   case DeclSpec::TST_enum:
   case DeclSpec::TST_union:
diff --git a/test/Sema/types.c b/test/Sema/types.c
index 7ab4e06..1232e47 100644
--- a/test/Sema/types.c
+++ b/test/Sema/types.c
@@ -30,3 +30,7 @@
 enum e { e_1 };
 extern int j[sizeof(enum e)];  // expected-note {{previous definition}}
 int j[42];   // expected-error {{redefinition of 'j' with a different type}}
+
+// rdar://6880104
+_Decimal32 x;  // expected-error {{GNU decimal type extension not supported}}
+