diff --git a/configure.ac b/configure.ac
index 88c0adbae..b2576b013 100644
--- a/configure.ac
+++ b/configure.ac
@@ -77,7 +77,7 @@ grub_TRANSFORM([grub-file])
 
 # Optimization flag.  Allow user to override.
 if test "x$TARGET_CFLAGS" = x; then
-  TARGET_CFLAGS="$TARGET_CFLAGS -Os"
+  TARGET_CFLAGS=-Os
 fi
 
 # Default HOST_CPPFLAGS