diff --git a/Firmware/planner.h b/Firmware/planner.h
index 2096111ea..5978793be 100644
--- a/Firmware/planner.h
+++ b/Firmware/planner.h
@@ -77,8 +77,8 @@ typedef struct {
   unsigned char direction_bits;             // The direction bit set for this block (refers to *_DIRECTION_BIT in config.h)
   unsigned char active_extruder;            // Selects the active extruder
   // accelerate_until and decelerate_after are set by calculate_trapezoid_for_block() and they need to be synchronized with the stepper interrupt controller.
-  long accelerate_until;                    // The index of the step event on which to stop acceleration
-  long decelerate_after;                    // The index of the step event on which to start decelerating
+  uint32_t accelerate_until;                    // The index of the step event on which to stop acceleration
+  uint32_t decelerate_after;                    // The index of the step event on which to start decelerating
 
   // Fields used by the motion planner to manage acceleration
 //  float speed_x, speed_y, speed_z, speed_e;        // Nominal mm/sec for each axis
@@ -100,13 +100,12 @@ typedef struct {
 
   // Settings for the trapezoid generator (runs inside an interrupt handler).
   // Changing the following values in the planner needs to be synchronized with the interrupt handler by disabling the interrupts.
-  //FIXME nominal_rate, initial_rate and final_rate are limited to uint16_t by MultiU24X24toH16 in the stepper interrupt anyway!
   unsigned long nominal_rate;                        // The nominal step rate for this block in step_events/sec 
   unsigned long initial_rate;                        // The jerk-adjusted step rate at start of block  
   unsigned long final_rate;                          // The minimal rate at exit
   unsigned long acceleration_st;                     // acceleration steps/sec^2
-  //FIXME does it have to be unsigned long? Probably uint8_t would be just fine.
-  unsigned long fan_speed;
+  //FIXME does it have to be int? Probably uint8_t would be just fine. Need to change in other places as well
+  int fan_speed;
   volatile char busy;
 
 
diff --git a/Firmware/stepper.cpp b/Firmware/stepper.cpp
index de250ec97..5f72b5bd2 100644
--- a/Firmware/stepper.cpp
+++ b/Firmware/stepper.cpp
@@ -71,8 +71,7 @@ static dda_isteps_t
                counter_z,
                counter_e;
 volatile dda_usteps_t step_events_completed; // The number of step events executed in the current block
-static int32_t  acceleration_time, deceleration_time;
-//static unsigned long accelerate_until, decelerate_after, acceleration_rate, initial_rate, final_rate, nominal_rate;
+static uint32_t  acceleration_time, deceleration_time;
 static uint16_t acc_step_rate; // needed for deccelaration start point
 static uint8_t  step_loops;
 static uint16_t OCR1A_nominal;
@@ -799,7 +798,7 @@ FORCE_INLINE void isr() {
     // 25.12us for acceleration / deceleration.
     {
       //WRITE_NC(LOGIC_ANALYZER_CH1, true);
-      if (step_events_completed.wide <= (unsigned long int)current_block->accelerate_until) {
+      if (step_events_completed.wide <= current_block->accelerate_until) {
         // v = t * a   ->   acc_step_rate = acceleration_time * current_block->acceleration_rate
         MultiU24X24toH16(acc_step_rate, acceleration_time, current_block->acceleration_rate);
         acc_step_rate += uint16_t(current_block->initial_rate);
@@ -817,12 +816,12 @@ FORCE_INLINE void isr() {
         }
 #endif
       }
-      else if (step_events_completed.wide > (unsigned long int)current_block->decelerate_after) {
+      else if (step_events_completed.wide > current_block->decelerate_after) {
         uint16_t step_rate;
         MultiU24X24toH16(step_rate, deceleration_time, current_block->acceleration_rate);
         step_rate = acc_step_rate - step_rate; // Decelerate from aceleration end point.
-        if ((step_rate & 0x8000) || step_rate < uint16_t(current_block->final_rate)) {
-          // Result is negative or too small.
+        if (step_rate < uint16_t(current_block->final_rate)) {
+          // Result is too small.
           step_rate = uint16_t(current_block->final_rate);
         }
         // Step_rate to timer interval.
@@ -832,7 +831,7 @@ FORCE_INLINE void isr() {
 
 #ifdef LIN_ADVANCE
         if (current_block->use_advance_lead) {
-            if (step_events_completed.wide <= (unsigned long int)current_block->decelerate_after + step_loops) {
+            if (step_events_completed.wide <= current_block->decelerate_after + step_loops) {
                 target_adv_steps = current_block->final_adv_steps;
                 la_state = ADV_INIT | ADV_ACC_VARY;
             }