diff --git a/armsrc/appmain.c b/armsrc/appmain.c
index 053abf0d9..bc1b59ea2 100644
--- a/armsrc/appmain.c
+++ b/armsrc/appmain.c
@@ -1141,7 +1141,7 @@ static void PacketReceived(PacketCommandNG *packet) {
             break;
         }
         case CMD_LF_EM4X50_CHK: {
-            em4x50_chk((uint32_t *)packet->data.asBytes);
+            em4x50_chk((uint8_t *)packet->data.asBytes);
             break;
         }
 #endif
diff --git a/armsrc/em4x50.h b/armsrc/em4x50.h
index 9b029647d..33c18e794 100644
--- a/armsrc/em4x50.h
+++ b/armsrc/em4x50.h
@@ -26,6 +26,6 @@ void em4x50_brute(em4x50_data_t *etd);
 void em4x50_login(uint32_t *password);
 void em4x50_sim(void);
 void em4x50_reader(void);
-void em4x50_chk(uint32_t *numkeys);
+void em4x50_chk(uint8_t *filename);
 
 #endif /* EM4X50_H */