diff --git a/fido2/u2f.c b/fido2/u2f.c
index 1e94f56..0bcd9b7 100644
--- a/fido2/u2f.c
+++ b/fido2/u2f.c
@@ -225,7 +225,7 @@ static int16_t u2f_authenticate(struct u2f_authenticate_request * req, uint8_t c
     }
 
     count = ctap_atomic_count(0);
-    hash[0] = 0xff;
+    hash[0] = (count >> 24) & 0xff;
     hash[1] = (count >> 16) & 0xff;
     hash[2] = (count >> 8) & 0xff;
     hash[3] = (count >> 0) & 0xff;
@@ -242,7 +242,7 @@ static int16_t u2f_authenticate(struct u2f_authenticate_request * req, uint8_t c
     crypto_ecc256_sign(hash, 32, sig);
 
     u2f_response_writeback(&up,1);
-    hash[0] = 0xff;
+    hash[0] = (count >> 24) & 0xff;
     hash[1] = (count >> 16) & 0xff;
     hash[2] = (count >> 8) & 0xff;
     hash[3] = (count >> 0) & 0xff;