diff --git a/drivers/mfd/db8500-prcmu.c b/drivers/mfd/db8500-prcmu.c
index 95498f80c905..cb58e44b1e45 100644
--- a/drivers/mfd/db8500-prcmu.c
+++ b/drivers/mfd/db8500-prcmu.c
@@ -1745,6 +1745,7 @@ int prcmu_abb_write(u8 slave, u8 reg, u8 *value, u8 size)
 void prcmu_ac_wake_req(void)
 {
 	u32 val;
+	u32 status;
 
 	mutex_lock(&mb0_transfer.ac_wake_lock);
 
@@ -1754,11 +1755,34 @@ void prcmu_ac_wake_req(void)
 
 	atomic_set(&ac_wake_req_state, 1);
 
+retry:
 	writel((val | PRCM_HOSTACCESS_REQ_HOSTACCESS_REQ), PRCM_HOSTACCESS_REQ);
 
 	if (!wait_for_completion_timeout(&mb0_transfer.ac_wake_work,
-			msecs_to_jiffies(20000))) {
-		pr_err("prcmu: %s timed out (20 s) waiting for a reply.\n",
+			msecs_to_jiffies(5000))) {
+		panic("prcmu: %s timed out (5 s) waiting for a reply.\n",
+			__func__);
+		goto unlock_and_return;
+	}
+
+	/*
+	 * The modem can generate an AC_WAKE_ACK, and then still go to sleep.
+	 * As a workaround, we wait, and then check that the modem is indeed
+	 * awake (in terms of the value of the PRCM_MOD_AWAKE_STATUS
+	 * register, which may not be the whole truth).
+	 */
+	udelay(400);
+	status = (readl(PRCM_MOD_AWAKE_STATUS) & BITS(0, 2));
+	if (status != (PRCM_MOD_AWAKE_STATUS_PRCM_MOD_AAPD_AWAKE |
+			PRCM_MOD_AWAKE_STATUS_PRCM_MOD_COREPD_AWAKE)) {
+		pr_err("prcmu: %s received ack, but modem not awake (0x%X).\n",
+			__func__, status);
+		udelay(1200);
+		writel(val, PRCM_HOSTACCESS_REQ);
+		if (wait_for_completion_timeout(&mb0_transfer.ac_wake_work,
+				msecs_to_jiffies(5000)))
+			goto retry;
+		panic("prcmu: %s timed out (5 s) waiting for AC_SLEEP_ACK.\n",
 			__func__);
 	}
 
@@ -1783,8 +1807,8 @@ void prcmu_ac_sleep_req()
 		PRCM_HOSTACCESS_REQ);
 
 	if (!wait_for_completion_timeout(&mb0_transfer.ac_wake_work,
-			msecs_to_jiffies(20000))) {
-		pr_err("prcmu: %s timed out (20 s) waiting for a reply.\n",
+			msecs_to_jiffies(5000))) {
+		panic("prcmu: %s timed out (5 s) waiting for a reply.\n",
 			__func__);
 	}