diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
index 4a9f3492b921..70a770ac0138 100644
--- a/drivers/char/hpet.c
+++ b/drivers/char/hpet.c
@@ -166,9 +166,8 @@ static irqreturn_t hpet_interrupt(int irq, void *data)
 		unsigned long m, t;
 
 		t = devp->hd_ireqfreq;
-		m = read_counter(&devp->hd_hpet->hpet_mc);
-		write_counter(t + m + devp->hd_hpets->hp_delta,
-			      &devp->hd_timer->hpet_compare);
+		m = read_counter(&devp->hd_timer->hpet_compare);
+		write_counter(t + m, &devp->hd_timer->hpet_compare);
 	}
 
 	if (devp->hd_flags & HPET_SHARED_IRQ)
@@ -504,21 +503,25 @@ static int hpet_ioctl_ieon(struct hpet_dev *devp)
 	g = v | Tn_32MODE_CNF_MASK | Tn_INT_ENB_CNF_MASK;
 
 	if (devp->hd_flags & HPET_PERIODIC) {
-		write_counter(t, &timer->hpet_compare);
 		g |= Tn_TYPE_CNF_MASK;
-		v |= Tn_TYPE_CNF_MASK;
-		writeq(v, &timer->hpet_config);
-		v |= Tn_VAL_SET_CNF_MASK;
+		v |= Tn_TYPE_CNF_MASK | Tn_VAL_SET_CNF_MASK;
 		writeq(v, &timer->hpet_config);
 		local_irq_save(flags);
 
-		/* NOTE:  what we modify here is a hidden accumulator
+		/*
+		 * NOTE: First we modify the hidden accumulator
 		 * register supported by periodic-capable comparators.
 		 * We never want to modify the (single) counter; that
-		 * would affect all the comparators.
+		 * would affect all the comparators. The value written
+		 * is the counter value when the first interrupt is due.
 		 */
 		m = read_counter(&hpet->hpet_mc);
 		write_counter(t + m + hpetp->hp_delta, &timer->hpet_compare);
+		/*
+		 * Then we modify the comparator, indicating the period
+		 * for subsequent interrupt.
+		 */
+		write_counter(t, &timer->hpet_compare);
 	} else {
 		local_irq_save(flags);
 		m = read_counter(&hpet->hpet_mc);