diff --git a/src/vim9compile.c b/src/vim9compile.c
index e2e5b76..d45dd63 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -291,7 +291,7 @@
  * Return TRUE if the script context is Vim9 script.
  */
     int
-script_is_vim9()
+script_is_vim9(void)
 {
     return SCRIPT_ITEM(current_sctx.sc_sid)->sn_version == SCRIPT_VERSION_VIM9;
 }