diff --git a/src/indent.c b/src/indent.c
index 477a44d..be4d563 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -1161,7 +1161,7 @@
  * Return TRUE if the conditions are OK for smart indenting.
  */
     int
-may_do_si()
+may_do_si(void)
 {
     return curbuf->b_p_si
 	&& !curbuf->b_p_cin