diff --git a/test/Headers/ms-intrin.cpp b/test/Headers/ms-intrin.cpp
index 58ad5a2449cab98cb47e24251fdfaee9418dab57..0a2c9201a4c6f2947ba49b3b1a6c23e8b9336b0c 100644
--- a/test/Headers/ms-intrin.cpp
+++ b/test/Headers/ms-intrin.cpp
@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -triple i386-pc-win32 -target-cpu pentium4 \
 // RUN:     -fms-extensions -fms-compatibility -fmsc-version=1700 \
-// RUN:     -ffreestanding -fsyntax-only %s
+// RUN:     -ffreestanding -fsyntax-only -Werror %s
 
 // Intrin.h needs size_t, but -ffreestanding prevents us from getting it from
 // stddef.h.  Work around it with this typedef.