diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 7bac408..865e18b 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -388,7 +388,7 @@
 
     msg "build: ARM Compiler 6 ($FLAGS)"
     ARM_TOOL_VARIANT="ult" CC="$ARMC6_CC" AR="$ARMC6_AR" CFLAGS="$FLAGS" \
-                    WARNING_CFLAGS='-xc -std=c99' make lib
+                    WARNING_CFLAGS='-Werror -xc -std=c99' make lib
 
     msg "size: ARM Compiler 6 ($FLAGS)"
     "$ARMC6_FROMELF" -z library/*.o