diff --git a/armsrc/iso14443a.c b/armsrc/iso14443a.c
index a22a79390..023eb02f9 100644
--- a/armsrc/iso14443a.c
+++ b/armsrc/iso14443a.c
@@ -2747,7 +2747,7 @@ void DetectNACKbug() {
     bool received_nack;
 
     // Mifare Classic's random generator repeats every 2^16 cycles (and so do the nonces).
-    uint32_t sync_cycles = PRNG_SEQUENCE_LENGTH;
+    int32_t sync_cycles = PRNG_SEQUENCE_LENGTH;
 
     BigBuf_free();
     BigBuf_Clear_ext(false);