diff --git a/radio/src/rtos.h b/radio/src/rtos.h
index 1478b778a..d352b953a 100644
--- a/radio/src/rtos.h
+++ b/radio/src/rtos.h
@@ -27,8 +27,6 @@
 extern "C++" {
 #endif
 
-#define doNothing()                     do { } while(0)   // seems unused? don't ever use this with SIMU
-
 #if defined(SIMU)
 
   #include <pthread.h>
@@ -149,7 +147,7 @@ extern "C++" {
   }
 #endif
 
-  #define RTOS_MS_PER_TICK              (CFG_CPU_FREQ / CFG_SYSTICK_FREQ / (CFG_CPU_FREQ / 1000))  // RTOS timer tick length in ms (currently 2)
+  #define RTOS_MS_PER_TICK              ((CFG_CPU_FREQ / CFG_SYSTICK_FREQ) / (CFG_CPU_FREQ / 1000))  // RTOS timer tick length in ms (currently 2)
 
   typedef OS_TID RTOS_TASK_HANDLE;
   typedef OS_MutexID RTOS_MUTEX_HANDLE;
diff --git a/radio/src/tasks_arm.cpp b/radio/src/tasks_arm.cpp
index fdfa36f0c..129684a4d 100644
--- a/radio/src/tasks_arm.cpp
+++ b/radio/src/tasks_arm.cpp
@@ -122,7 +122,7 @@ TASK_FUNCTION(mixerTask)
 
     if (!s_pulses_paused) {
       uint16_t t0 = getTmr2MHz();
-      
+
       DEBUG_TIMER_START(debugTimerMixer);
       RTOS_LOCK_MUTEX(mixerMutex);
       doMixerCalculations();
@@ -162,11 +162,11 @@ void scheduleNextMixerCalculation(uint8_t module, uint16_t period_ms)
 {
   // Schedule next mixer calculation time,
   // for now assume mixer calculation takes 2 ms.
-  nextMixerTime[module] = (uint32_t)RTOS_GET_TIME() + period_ms - 1 /*1.2ms before next pulse*/;
+  nextMixerTime[module] = (uint32_t)RTOS_GET_TIME() + (period_ms / RTOS_MS_PER_TICK) - 1 /* 1 tick in advance*/;
   DEBUG_TIMER_STOP(debugTimerMixerCalcToUsage);
 }
 
-#define MENU_TASK_PERIOD_TICKS      50    // 50ms
+#define MENU_TASK_PERIOD_TICKS         (50 / RTOS_MS_PER_TICK)    // 50ms
 
 #if defined(COLORLCD) && defined(CLI)
 bool perMainEnabled = true;