diff --git a/main.c b/main.c
index 78e21ad..9608211 100644
--- a/main.c
+++ b/main.c
@@ -33,7 +33,7 @@ static void usage(int argc, char **argv, char *message, ...) {
         va_end(args);
     }
 
-    fprintf(stderr, "usage: %s file\n", argv[0]);
+    fprintf(stderr, "usage: %s [file]\n", argv[0]);
     exit(1);
 }