diff --git a/include/arm11/hardware/timer.h b/include/arm11/hardware/timer.h
index a7338cd..dccd092 100644
--- a/include/arm11/hardware/timer.h
+++ b/include/arm11/hardware/timer.h
@@ -29,7 +29,7 @@
 #define TIMER_IRQ_ENABLE   (1u<<2)
 
 // p is the prescaler value and n the frequence
-#define TIMER_FREQ(p, n)   (TIMER_BASE_FREQ / 2 / ((p) + 1) / (n))
+#define TIMER_FREQ(p, n)   (TIMER_BASE_FREQ / 2 / (p) / (n))
 
 
 
diff --git a/source/arm11/hardware/timer.c b/source/arm11/hardware/timer.c
index 2d21495..b5a5445 100644
--- a/source/arm11/hardware/timer.c
+++ b/source/arm11/hardware/timer.c
@@ -20,6 +20,7 @@
 #include "mem_map.h"
 #include "arm11/hardware/timer.h"
 #include "arm11/hardware/interrupt.h"
+#include "fb_assert.h"
 #include "arm11/event.h"
 
 
@@ -41,8 +42,10 @@
 
 void TIMER_start(u8 prescaler, u32 ticks, bool autoReload, bool enableIrq)
 {
+	fb_assert(prescaler > 0);
+
 	REG_TIMER_LOAD = ticks;
-	REG_TIMER_CNT = prescaler<<8 | (enableIrq ? TIMER_IRQ_ENABLE : 0) |
+	REG_TIMER_CNT = (prescaler - 1)<<8 | (enableIrq ? TIMER_IRQ_ENABLE : 0) |
 	                (autoReload ? TIMER_AUTO_RELOAD : TIMER_SINGLE_SHOT) | TIMER_ENABLE;
 }
 
@@ -60,7 +63,7 @@
 void TIMER_sleepTicks(u32 ticks)
 {
 	REG_TIMER_LOAD = ticks;
-	REG_TIMER_CNT = 0u<<8 | TIMER_IRQ_ENABLE | TIMER_SINGLE_SHOT | TIMER_ENABLE;
+	REG_TIMER_CNT = TIMER_IRQ_ENABLE | TIMER_SINGLE_SHOT | TIMER_ENABLE;
 
 	while(REG_TIMER_COUNTER) __wfe();