diff --git a/include/libopencm3/stm32/timer.h b/include/libopencm3/stm32/timer.h
index 71ff64cd..54cc2284 100644
--- a/include/libopencm3/stm32/timer.h
+++ b/include/libopencm3/stm32/timer.h
@@ -857,8 +857,8 @@ void timer_enable_irq(u32 timer_peripheral, u32 irq);
 void timer_disable_irq(u32 timer_peripheral, u32 irq);
 bool timer_get_flag(u32 timer_peripheral, u32 flag);
 void timer_clear_flag(u32 timer_peripheral, u32 flag);
-void timer_set_mode(u32 timer_peripheral, u8 clock_div,
-		    u8 alignment, u8 direction);
+void timer_set_mode(u32 timer_peripheral, u32 clock_div,
+		    u32 alignment, u32 direction);
 void timer_set_clock_division(u32 timer_peripheral, u32 clock_div);
 void timer_enable_preload(u32 timer_peripheral);
 void timer_disable_preload(u32 timer_peripheral);
diff --git a/lib/stm32/f1/timer.c b/lib/stm32/f1/timer.c
index 8c32670e..85f81ea4 100644
--- a/lib/stm32/f1/timer.c
+++ b/lib/stm32/f1/timer.c
@@ -118,8 +118,8 @@ void timer_clear_flag(u32 timer_peripheral, u32 flag)
 	TIM_SR(timer_peripheral) &= ~flag;
 }
 
-void timer_set_mode(u32 timer_peripheral, u8 clock_div,
-		    u8 alignment, u8 direction)
+void timer_set_mode(u32 timer_peripheral, u32 clock_div,
+		    u32 alignment, u32 direction)
 {
 	u32 cr1;
 
diff --git a/lib/stm32/f2/timer.c b/lib/stm32/f2/timer.c
index 3cd5e919..659f8a99 100644
--- a/lib/stm32/f2/timer.c
+++ b/lib/stm32/f2/timer.c
@@ -119,8 +119,8 @@ void timer_clear_flag(u32 timer_peripheral, u32 flag)
 	TIM_SR(timer_peripheral) &= ~flag;
 }
 
-void timer_set_mode(u32 timer_peripheral, u8 clock_div,
-		    u8 alignment, u8 direction)
+void timer_set_mode(u32 timer_peripheral, u32 clock_div,
+		    u32 alignment, u32 direction)
 {
 	u32 cr1;
 
diff --git a/lib/stm32/f4/timer.c b/lib/stm32/f4/timer.c
index bb7b0e7e..6d5ab9df 100644
--- a/lib/stm32/f4/timer.c
+++ b/lib/stm32/f4/timer.c
@@ -119,8 +119,8 @@ void timer_clear_flag(u32 timer_peripheral, u32 flag)
 	TIM_SR(timer_peripheral) &= ~flag;
 }
 
-void timer_set_mode(u32 timer_peripheral, u8 clock_div,
-		    u8 alignment, u8 direction)
+void timer_set_mode(u32 timer_peripheral, u32 clock_div,
+		    u32 alignment, u32 direction)
 {
 	u32 cr1;