diff --git a/tools/mfd_aes_brute/brute_key.c b/tools/mfd_aes_brute/brute_key.c
index 5db3feded..58fdb86d5 100644
--- a/tools/mfd_aes_brute/brute_key.c
+++ b/tools/mfd_aes_brute/brute_key.c
@@ -107,7 +107,7 @@ int main (int argc, char* argv[]) {
     uint8_t tag_challenge[16]  = {0x00};
     uint8_t lock_challenge[32] = {0x00};
 
-    int timestamp = atoi(argv[1]);
+    uint64_t timestamp = atoi(argv[1]);
 
     if (argc != 4) {
         printf("\nusage: %s <unix timestamp> <16 byte tag challenge> <32 byte lock challenge>\n\n", argv[0]);
@@ -120,7 +120,7 @@ int main (int argc, char* argv[]) {
     if(hexstr_to_byte_array(argv[3], lock_challenge, sizeof(lock_challenge)))
         return 3;
 
-    int start_time = time(NULL);
+    uint64_t start_time = time(NULL);
 
     for (; timestamp < start_time; timestamp++) {