diff --git a/hw/timer/exynos4210_pwm.c b/hw/timer/exynos4210_pwm.c
index aa5dca68ef..59a8c08db0 100644
--- a/hw/timer/exynos4210_pwm.c
+++ b/hw/timer/exynos4210_pwm.c
@@ -25,7 +25,6 @@
 #include "hw/sysbus.h"
 #include "migration/vmstate.h"
 #include "qemu/timer.h"
-#include "qemu/main-loop.h"
 #include "qemu/module.h"
 #include "hw/ptimer.h"
 
@@ -150,7 +149,9 @@ static const VMStateDescription vmstate_exynos4210_pwm_state = {
 };
 
 /*
- * PWM update frequency
+ * PWM update frequency.
+ * Must be called within a ptimer_transaction_begin/commit block
+ * for s->timer[id].ptimer.
  */
 static void exynos4210_pwm_update_freq(Exynos4210PWMState *s, uint32_t id)
 {
@@ -281,12 +282,15 @@ static void exynos4210_pwm_write(void *opaque, hwaddr offset,
 
         /* update timers frequencies */
         for (i = 0; i < EXYNOS4210_PWM_TIMERS_NUM; i++) {
+            ptimer_transaction_begin(s->timer[i].ptimer);
             exynos4210_pwm_update_freq(s, s->timer[i].id);
+            ptimer_transaction_commit(s->timer[i].ptimer);
         }
         break;
 
     case TCON:
         for (i = 0; i < EXYNOS4210_PWM_TIMERS_NUM; i++) {
+            ptimer_transaction_begin(s->timer[i].ptimer);
             if ((value & TCON_TIMER_MANUAL_UPD(i)) >
             (s->reg_tcon & TCON_TIMER_MANUAL_UPD(i))) {
                 /*
@@ -315,6 +319,7 @@ static void exynos4210_pwm_write(void *opaque, hwaddr offset,
                 ptimer_stop(s->timer[i].ptimer);
                 DPRINTF("stop timer %d\n", i);
             }
+            ptimer_transaction_commit(s->timer[i].ptimer);
         }
         s->reg_tcon = value;
         break;
@@ -369,8 +374,10 @@ static void exynos4210_pwm_reset(DeviceState *d)
         s->timer[i].reg_tcmpb = 0;
         s->timer[i].reg_tcntb = 0;
 
+        ptimer_transaction_begin(s->timer[i].ptimer);
         exynos4210_pwm_update_freq(s, s->timer[i].id);
         ptimer_stop(s->timer[i].ptimer);
+        ptimer_transaction_commit(s->timer[i].ptimer);
     }
 }
 
@@ -388,12 +395,12 @@ static void exynos4210_pwm_init(Object *obj)
     Exynos4210PWMState *s = EXYNOS4210_PWM(obj);
     SysBusDevice *dev = SYS_BUS_DEVICE(obj);
     int i;
-    QEMUBH *bh;
 
     for (i = 0; i < EXYNOS4210_PWM_TIMERS_NUM; i++) {
-        bh = qemu_bh_new(exynos4210_pwm_tick, &s->timer[i]);
         sysbus_init_irq(dev, &s->timer[i].irq);
-        s->timer[i].ptimer = ptimer_init_with_bh(bh, PTIMER_POLICY_DEFAULT);
+        s->timer[i].ptimer = ptimer_init(exynos4210_pwm_tick,
+                                         &s->timer[i],
+                                         PTIMER_POLICY_DEFAULT);
         s->timer[i].id = i;
         s->timer[i].parent = s;
     }