diff --git a/src/crcspeed.c b/src/crcspeed.c
index d2d97a8c7..81a80ce8e 100644
--- a/src/crcspeed.c
+++ b/src/crcspeed.c
@@ -35,7 +35,8 @@ void crcspeed64little_init(crcfn64 crcfn, uint64_t table[8][256]) {
 
     /* generate CRCs for all single byte sequences */
     for (int n = 0; n < 256; n++) {
-        table[0][n] = crcfn(0, &n, 1);
+        unsigned char v = n;
+        table[0][n] = crcfn(0, &v, 1);
     }
 
     /* generate nested CRC table for future slice-by-8 lookup */