diff --git a/armsrc/mifareutil.c b/armsrc/mifareutil.c
index e94d09f40..5dfbfd26b 100644
--- a/armsrc/mifareutil.c
+++ b/armsrc/mifareutil.c
@@ -139,7 +139,7 @@ int mifare_classic_auth(struct Crypto1State *pcs, uint32_t uid, uint8_t blockNo,
     return mifare_classic_authex(pcs, uid, blockNo, keyType, ui64Key, isNested, NULL, NULL);
 }
 int mifare_classic_authex(struct Crypto1State *pcs, uint32_t uid, uint8_t blockNo, uint8_t keyType, uint64_t ui64Key, uint8_t isNested, uint32_t *ntptr, uint32_t *timing) {
-    return mifare_classic_authex_cmd(pcs, uid, blockNo, keyType ? MIFARE_AUTH_KEYA : MIFARE_AUTH_KEYB, ui64Key, isNested, ntptr, timing);
+    return mifare_classic_authex_cmd(pcs, uid, blockNo, (keyType & 1) == 0 ? MIFARE_AUTH_KEYA : MIFARE_AUTH_KEYB, ui64Key, isNested, ntptr, timing);
 }
 int mifare_classic_authex_cmd(struct Crypto1State *pcs, uint32_t uid, uint8_t blockNo, uint8_t cmd, uint64_t ui64Key, uint8_t isNested, uint32_t *ntptr, uint32_t *timing) {