diff --git a/src/kernel/race.c b/src/kernel/race.c
index c57d98a24..c7c2e8165 100644
--- a/src/kernel/race.c
+++ b/src/kernel/race.c
@@ -94,7 +94,8 @@ enum {
     RCO_TRADEHERB,
 };
 
-static void rc_setoption(race *rc, int key, const char *value) {
+static void rc_setoption(race *rc, int k, const char *value) {
+    unsigned char key = (unsigned char)k;
     int i;
     variant *v = NULL;
     if (!rc->options) {