diff --git a/src/lib9/main.c b/src/lib9/main.c
index 85a73f9f29..f1bde9c95f 100644
--- a/src/lib9/main.c
+++ b/src/lib9/main.c
@@ -30,7 +30,8 @@ THE SOFTWARE.
 #ifdef WIN32
 #include <windows.h>
 
-static void crashhandler() {
+static void crashhandler(int sig) {
+	USED(sig);
 	fprint(2, "%s: internal fatal error.\n", argv0);
 	exit(1);
 }