diff --git a/client/src/mifare/desfirecrypto.c b/client/src/mifare/desfirecrypto.c
index 187744ec7..8960b8b96 100644
--- a/client/src/mifare/desfirecrypto.c
+++ b/client/src/mifare/desfirecrypto.c
@@ -265,6 +265,7 @@ void DesfireCryptoCMAC(DesfireContext *ctx, uint8_t *data, size_t len, uint8_t *
 
     DesfireCryptoEncDec(ctx, true, buffer, len, NULL, true);
 
-    memcpy(cmac, ctx->IV, kbs);
+    if (cmac != NULL)
+        memcpy(cmac, ctx->IV, kbs);
 }