diff --git a/grbl/planner.h b/grbl/planner.h
index 306f9d91..ac892541 100644
--- a/grbl/planner.h
+++ b/grbl/planner.h
@@ -60,7 +60,12 @@ typedef struct {
   // NOTE: Used by stepper algorithm to execute the block correctly. Do not alter these values.
   uint32_t steps[N_AXIS];    // Step count along each axis
   uint32_t step_event_count; // The maximum step axis count and number of steps required to complete this block.
-  uint16_t direction_bits;    // The direction bit set for this block (refers to *_DIRECTION_BIT in config.h)
+
+  #ifdef STM32F103C8
+    uint16_t direction_bits;    // The direction bit set for this block (refers to *_DIRECTION_BIT in config.h)
+  #else
+    uint8_t direction_bits;    // The direction bit set for this block (refers to *_DIRECTION_BIT in config.h)
+  #endif
 
   // Block condition data to ensure correct execution depending on states and overrides.
   uint8_t condition;      // Block bitflag variable defining block run conditions. Copied from pl_line_data.
diff --git a/grbl/spindle_control.c b/grbl/spindle_control.c
index 4e18cf86..b234a7fe 100644
--- a/grbl/spindle_control.c
+++ b/grbl/spindle_control.c
@@ -107,7 +107,12 @@ void spindle_init()
 
 uint8_t spindle_get_state()
 {
-  uint16_t pin = 0;
+  #if defined (STM32F103C8)
+    uint16_t pin = 0;
+  #else
+    uint8_t pin = 0;
+  #endif
+
 	#ifdef VARIABLE_SPINDLE
     #ifdef USE_SPINDLE_DIR_AS_ENABLE_PIN
 #ifdef AVRTARGET
@@ -116,7 +121,7 @@ uint8_t spindle_get_state()
 #if defined (STM32F103C8)
   pin = GPIO_ReadInputData(SPINDLE_ENABLE_PORT);
 #endif
-		  // No spindle direction output pin. 
+		  // No spindle direction output pin.
 			#ifdef INVERT_SPINDLE_ENABLE_PIN
 			  if (bit_isfalse(pin,(1<<SPINDLE_ENABLE_BIT))) { return(SPINDLE_STATE_CW); }
 	    #else
@@ -125,7 +130,7 @@ uint8_t spindle_get_state()
     #else
 #ifdef AVRTARGET
   pin = SPINDLE_DIRECTION_PORT;
-    if (SPINDLE_TCCRA_REGISTER & (1<<SPINDLE_COMB_BIT)) 
+    if (SPINDLE_TCCRA_REGISTER & (1<<SPINDLE_COMB_BIT))
 #endif
 #if defined (STM32F103C8)
       pin = GPIO_ReadInputData(SPINDLE_DIRECTION_PORT);
@@ -324,12 +329,12 @@ void spindle_stop()
 {
   if (sys.abort) { return; } // Block during abort.
   if (state == SPINDLE_DISABLE) { // Halt or set spindle direction and rpm.
-  
+
     #ifdef VARIABLE_SPINDLE
       sys.spindle_speed = 0.0f;
     #endif
     spindle_stop();
-  
+
   } else {
     #ifndef USE_SPINDLE_DIR_AS_ENABLE_PIN
       if (state == SPINDLE_ENABLE_CW) {
@@ -339,7 +344,7 @@ void spindle_stop()
       SetSpindleDirectionBit();
       }
     #endif
-  
+
     #ifdef VARIABLE_SPINDLE
       // NOTE: Assumes all calls to this function is when Grbl is not moving or must remain off.
       if (settings.flags & BITFLAG_LASER_MODE) {
@@ -355,15 +360,15 @@ void spindle_stop()
         ResetSpindleEnablebit();
       #else
         SetSpindleEnablebit();
-      #endif    
+      #endif
     #endif
   }
-  
+
   sys.report_ovr_counter = 0; // Set to report change immediately
 }
 
 
-// G-code parser entry-point for setting spindle state. Forces a planner buffer sync and bails 
+// G-code parser entry-point for setting spindle state. Forces a planner buffer sync and bails
 // if an abort or check-mode is active.
 #ifdef VARIABLE_SPINDLE
   void spindle_sync(uint8_t state, float rpm)
diff --git a/grbl/stepper.c b/grbl/stepper.c
index 59e1840c..efc0d8f4 100644
--- a/grbl/stepper.c
+++ b/grbl/stepper.c
@@ -122,7 +122,11 @@ LONGLONG nTimer0Out = 0;
 typedef struct {
   uint32_t steps[N_AXIS];
   uint32_t step_event_count;
+ #ifdef STM32F103C8
   uint16_t direction_bits;
+ #else
+  unit8_t direction_bits;
+ #endif
   #ifdef VARIABLE_SPINDLE
     uint8_t is_pwm_rate_adjusted; // Tracks motions that require constant laser power/rate
   #endif
@@ -143,7 +147,11 @@ typedef struct {
     uint8_t prescaler;      // Without AMASS, a prescaler is required to adjust for slow timing.
   #endif
   #ifdef VARIABLE_SPINDLE
+   #ifdef STM32F103C8
     uint32_t spindle_pwm;
+   #else
+    uint8_t spindle_pwm;
+   #endif
   #endif
 } segment_t;
 static segment_t segment_buffer[SEGMENT_BUFFER_SIZE];
@@ -165,9 +173,14 @@ typedef struct {
   #endif
 
   #ifdef STEP_PULSE_DELAY
+  #ifdef STM32F103C8
+   uint16_t step_bits;
+  #else
     uint8_t step_bits;  // Stores out_bits output to complete the step pulse delay
   #endif
 
+  #endif
+
   uint8_t execute_step;     // Flags step execution for each interrupt.
 #ifndef WIN32
   uint8_t step_pulse_time;  // Step pulse reset time after step rise
@@ -233,7 +246,11 @@ typedef struct {
 
   #ifdef VARIABLE_SPINDLE
     float inv_rate;    // Used by PWM laser mode to speed up segment calculations.
-    uint32_t current_spindle_pwm;
+    #ifdef STM32F103C8
+      uint32_t current_spindle_pwm;
+    #else
+      uint8_t current_spindle_pwm;
+    #endif
   #endif
 } st_prep_t;
 static st_prep_t prep;
@@ -548,7 +565,7 @@ void Timer1Proc()
       #endif
 
       #ifdef VARIABLE_SPINDLE
-        // Set real-time spindle output as segment is loaded, just prior to the first step. CMMT 
+        // Set real-time spindle output as segment is loaded, just prior to the first step. CMMT
         spindle_set_speed(st.exec_segment->spindle_pwm);
       #endif