diff --git a/src/vim9compile.c b/src/vim9compile.c
index db24eae..c876da0 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -288,7 +288,7 @@
  * Return FAIL and give an error if it defined.
  */
     int
-check_defined(char_u *p, int len, cctx_T *cctx)
+check_defined(char_u *p, size_t len, cctx_T *cctx)
 {
     if (lookup_script(p, len) == OK
 	    || (cctx != NULL