diff --git a/m4/as-ac-expand.m4 b/m4/as-ac-expand.m4
index 89c90c0..2094019 100644
--- a/m4/as-ac-expand.m4
+++ b/m4/as-ac-expand.m4
@@ -22,7 +22,7 @@ AC_DEFUN([AS_AC_EXPAND],
   dnl loop until it doesn't change anymore
   while true; do
     new_full_var="`eval echo $full_var`"
-    if test "x$new_full_var"="x$full_var"; then break; fi
+    if test "x$new_full_var" == "x$full_var"; then break; fi
     full_var=$new_full_var
   done