diff --git a/armsrc/em4x50.h b/armsrc/em4x50.h
index 75f663db2..35c519a9e 100644
--- a/armsrc/em4x50.h
+++ b/armsrc/em4x50.h
@@ -29,7 +29,7 @@ void em4x50_login(uint32_t *password);
 void em4x50_reset(void);
 void em4x50_watch(void);
 void em4x50_restore(em4x50_data_t *etd);
-void em4x50_sim(em4x50_data_t *etd);
+void em4x50_sim(void);
 void em4x50_std_read(void);
 
 #endif /* EM4X50_H */