diff --git a/gc.c b/gc.c
index 68665fe..7952d1f 100644
--- a/gc.c
+++ b/gc.c
@@ -1536,7 +1536,7 @@ static void _fprint_value(FILE *f, value_t v, seen_value_t *seen)
   }
   else if (is_fixnum(v))
   {
-    fprintf(f, "%d", (int)get_fixnum(v));
+    fprintf(f, "%lld", (long long int)get_fixnum(v));
   }
   else if (is_box(v))
   {