diff --git a/st.c b/st.c
index 6ba467d..62def59 100644
--- a/st.c
+++ b/st.c
@@ -939,7 +939,7 @@ ttyresize(int tw, int th)
 }
 
 void
-ttyhangup()
+ttyhangup(void)
 {
 	/* Send SIGHUP to shell */
 	kill(pid, SIGHUP);