diff --git a/acinclude.m4 b/acinclude.m4
index 020f433fb63..dd475b28cf5 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -2048,7 +2048,8 @@ AC_DEFUN([PHP_PROG_LEX], [
   case $php_cv_flex_version in
     ""|invalid[)]
       flex_msg="flex versions supported for regeneration of the Zend/PHP parsers: $flex_version_list  (found: $flex_version)."
-      AC_MSG_ERROR([$flex_msg])
+      AC_MSG_WARN([$flex_msg])
+      LEX="echo \"error: $flex_msg\" 1>&2 ; exit 1;"
       ;;
   esac
   PHP_SUBST(LEX)