diff --git a/armsrc/hfops.c b/armsrc/hfops.c
index 6a97be76a..df42c8685 100644
--- a/armsrc/hfops.c
+++ b/armsrc/hfops.c
@@ -200,7 +200,7 @@ static uint32_t HfEncodeTkm(const uint8_t *uid, uint8_t modulation, uint8_t *dat
     return len;
 }
 
-int HfSimulateTkm(uint8_t *uid, uint8_t modulation, uint32_t timeout) {
+int HfSimulateTkm(const uint8_t *uid, uint8_t modulation, uint32_t timeout) {
     // free eventually allocated BigBuf memory
     BigBuf_free_keep_EM();
 
diff --git a/armsrc/hfops.h b/armsrc/hfops.h
index 352f9d2bc..c738887b4 100644
--- a/armsrc/hfops.h
+++ b/armsrc/hfops.h
@@ -22,6 +22,6 @@
 #include "common.h"
 
 int HfReadADC(uint32_t samplesCount, bool ledcontrol);
-int HfSimulateTkm(uint8_t *uid, uint8_t modulation, uint32_t timeout);
+int HfSimulateTkm(const uint8_t *uid, uint8_t modulation, uint32_t timeout);
 
 #endif