diff --git a/scheme/base.sld b/scheme/base.sld
index fff0534f..1d9c90e9 100644
--- a/scheme/base.sld
+++ b/scheme/base.sld
@@ -989,7 +989,7 @@
         char ch_buf[5];
         char_type c;
         int buflen, num_cp, len;
-        Cyc_check_int(data, count);
+        Cyc_check_fixnum(data, count);
         if (!obj_is_char(fill)) {
           Cyc_rt_raise2(data, \"Expected character buf received\", fill);
         }