diff --git a/mozilla/configure.in b/mozilla/configure.in
index 8992c5e8920..31f4dced3fd 100644
--- a/mozilla/configure.in
+++ b/mozilla/configure.in
@@ -2815,7 +2815,7 @@ MOZ_ARG_ENABLE_STRING(extensions,
         MOZ_EXTENSIONS=""
     elif test "$option" = "default"; then
         MOZ_EXTENSIONS="$MOZ_EXTENSIONS $MOZ_EXTENSIONS_DEFAULT"
-    elif test `echo "$option" | grep -c ^-`; then
+    elif test `echo "$option" | grep -c ^-` != 0; then
         option=`echo $option | sed 's/^-//'`
         MOZ_EXTENSIONS=`echo "$MOZ_EXTENSIONS" | sed "s/ ${option}//"`
     else