diff --git a/src/basecmd.c b/src/basecmd.c
index ab31efc2..2c9562b6 100644
--- a/src/basecmd.c
+++ b/src/basecmd.c
@@ -156,7 +156,7 @@ DECL_COMMAND(command_finalize_config, "finalize_config crc=%u");
 
 static struct timer group_timer;
 
-static uint8_t
+static uint_fast8_t
 group_end_event(struct timer *timer)
 {
     shutdown("Missed scheduling of next event");
diff --git a/src/endstop.c b/src/endstop.c
index 6f155cda..c8aa58e6 100644
--- a/src/endstop.c
+++ b/src/endstop.c
@@ -23,7 +23,7 @@ struct end_stop {
 enum { ESF_HOMING=1, ESF_REPORT=2 };
 
 // Timer callback for an end stop
-static uint8_t
+static uint_fast8_t
 end_stop_event(struct timer *t)
 {
     struct end_stop *e = container_of(t, struct end_stop, time);
diff --git a/src/gpiocmds.c b/src/gpiocmds.c
index 864d6526..a86e12c9 100644
--- a/src/gpiocmds.c
+++ b/src/gpiocmds.c
@@ -22,13 +22,13 @@ struct digital_out_s {
     uint8_t value, default_value;
 };
 
-static uint8_t
+static uint_fast8_t
 digital_end_event(struct timer *timer)
 {
     shutdown("Missed scheduling of next pin event");
 }
 
-static uint8_t
+static uint_fast8_t
 digital_out_event(struct timer *timer)
 {
     struct digital_out_s *d = container_of(timer, struct digital_out_s, timer);
@@ -103,10 +103,10 @@ enum {
     SPF_NEXT_ON=1<<4, SPF_NEXT_TOGGLING=1<<5, SPF_NEXT_CHECK_END=1<<6,
 };
 
-static uint8_t soft_pwm_load_event(struct timer *timer);
+static uint_fast8_t soft_pwm_load_event(struct timer *timer);
 
 // Normal pulse change event
-static uint8_t
+static uint_fast8_t
 soft_pwm_toggle_event(struct timer *timer)
 {
     struct soft_pwm_s *s = container_of(timer, struct soft_pwm_s, timer);
@@ -127,7 +127,7 @@ soft_pwm_toggle_event(struct timer *timer)
 }
 
 // Load next pwm settings
-static uint8_t
+static uint_fast8_t
 soft_pwm_load_event(struct timer *timer)
 {
     struct soft_pwm_s *s = container_of(timer, struct soft_pwm_s, timer);
diff --git a/src/sched.c b/src/sched.c
index 99e37dd6..6b9ec16f 100644
--- a/src/sched.c
+++ b/src/sched.c
@@ -25,7 +25,7 @@ static uint16_t millis;
 // also simplifies the timer code by ensuring there is always at least
 // one timer on the timer list and that there is always a timer not
 // more than 1 ms in the future.
-static uint8_t
+static uint_fast8_t
 ms_event(struct timer *t)
 {
     millis++;
@@ -154,7 +154,7 @@ sched_timer_kick(void)
     struct timer *t = timer_list;
     for (;;) {
         // Invoke timer callback
-        uint8_t res;
+        uint_fast8_t res;
         if (CONFIG_INLINE_STEPPER_HACK && likely(!t->func))
             res = stepper_event(t);
         else
diff --git a/src/sched.h b/src/sched.h
index be73ce65..aabb17b0 100644
--- a/src/sched.h
+++ b/src/sched.h
@@ -15,7 +15,7 @@
 // Timer structure for scheduling timed events (see sched_timer() )
 struct timer {
     struct timer *next;
-    uint8_t (*func)(struct timer*);
+    uint_fast8_t (*func)(struct timer*);
     uint32_t waketime;
 };
 
diff --git a/src/stepper.c b/src/stepper.c
index 0d4754f9..5b5203f1 100644
--- a/src/stepper.c
+++ b/src/stepper.c
@@ -35,7 +35,7 @@ enum { MF_DIR=1 };
 enum { SF_LAST_DIR=1, SF_NEXT_DIR=2, SF_INVERT_STEP=4, SF_HAVE_ADD=8 };
 
 // Setup a stepper for the next move in its queue
-static uint8_t
+static uint_fast8_t
 stepper_load_next(struct stepper *s)
 {
     struct move *m = s->first;
@@ -64,7 +64,7 @@ stepper_load_next(struct stepper *s)
 }
 
 // Timer callback - step the given stepper.
-uint8_t
+uint_fast8_t
 stepper_event(struct timer *t)
 {
     struct stepper *s = container_of(t, struct stepper, time);
@@ -78,7 +78,7 @@ stepper_event(struct timer *t)
             s->interval += s->add;
         return SF_RESCHEDULE;
     }
-    uint8_t ret = stepper_load_next(s);
+    uint_fast8_t ret = stepper_load_next(s);
     gpio_out_toggle(s->step_pin);
     return ret;
 }
diff --git a/src/stepper.h b/src/stepper.h
index 9a81b56e..f4019ae5 100644
--- a/src/stepper.h
+++ b/src/stepper.h
@@ -5,7 +5,7 @@
 
 enum { STEPPER_POSITION_BIAS=0x40000000 };
 
-uint8_t stepper_event(struct timer *t);
+uint_fast8_t stepper_event(struct timer *t);
 void command_config_stepper(uint32_t *args);
 struct stepper;
 uint32_t stepper_get_position(struct stepper *s);