diff --git a/racket/src/racket/src/regexp.c b/racket/src/racket/src/regexp.c
index 21cbb375bc..7b16b02c53 100644
--- a/racket/src/racket/src/regexp.c
+++ b/racket/src/racket/src/regexp.c
@@ -243,7 +243,7 @@ regcomp(char *expstr, rxpos exp, int explen, int pcre, Scheme_Object *handler)
   regcodemax = 0;
   regbackknown = NULL;
   regbackdepends = NULL;
-  regc(MAGIC);
+  regc((char)MAGIC);
   if (reg(0, &flags, 0, 0, PARSE_CASE_SENS | PARSE_SINGLE_LINE | (pcre ? PARSE_PCRE : 0)) == 0) {
     FAIL("unknown regexp failure (late)");
   }