diff --git a/runtime/macros/maze/mazeclean.c b/runtime/macros/maze/mazeclean.c
index 04dcebd..f0f0bb6 100644
--- a/runtime/macros/maze/mazeclean.c
+++ b/runtime/macros/maze/mazeclean.c
@@ -8,7 +8,7 @@
 
 char *M, A, Z, E = 40, line[80], T[3];
 int
-main (C)
+main (int C)
 {
   for (M = line + E, *line = A = scanf ("%d", &C); --E; line[E] = M[E] = E)
     printf ("._");