diff --git a/plat/juno/plat_pm.c b/plat/juno/plat_pm.c
index a390706..47338cf 100644
--- a/plat/juno/plat_pm.c
+++ b/plat/juno/plat_pm.c
@@ -85,6 +85,31 @@
 }
 
 /*******************************************************************************
+ * Juno handler called to check the validity of the power state parameter.
+ ******************************************************************************/
+int32_t juno_validate_power_state(unsigned int power_state)
+{
+	/* Sanity check the requested state */
+	if (psci_get_pstate_type(power_state) == PSTATE_TYPE_STANDBY) {
+		/*
+		 * It's possible to enter standby only on affinity level 0 i.e.
+		 * a cpu on the Juno. Ignore any other affinity level.
+		 */
+		if (psci_get_pstate_afflvl(power_state) != MPIDR_AFFLVL0)
+			return PSCI_E_INVALID_PARAMS;
+	}
+
+	/*
+	 * We expect the 'state id' to be zero.
+	 */
+	if (psci_get_pstate_id(power_state))
+		return PSCI_E_INVALID_PARAMS;
+
+	return PSCI_E_SUCCESS;
+}
+
+
+/*******************************************************************************
  * Juno handler called when an affinity instance is about to be turned on. The
  * level and mpidr determine the affinity instance.
  ******************************************************************************/
@@ -118,13 +143,13 @@
  * was turned off prior to wakeup and do what's necessary to setup it up
  * correctly.
  ******************************************************************************/
-int32_t juno_affinst_on_finish(uint32_t afflvl, uint32_t state)
+void juno_affinst_on_finish(uint32_t afflvl, uint32_t state)
 {
 	unsigned long mpidr;
 
 	/* Determine if any platform actions need to be executed. */
 	if (juno_do_plat_actions(afflvl, state) == -EAGAIN)
-		return PSCI_E_SUCCESS;
+		return;
 
 	/* Get the mpidr for this cpu */
 	mpidr = read_mpidr_el1();
@@ -145,8 +170,6 @@
 
 	/* Clear the mailbox for this cpu. */
 	juno_program_mailbox(mpidr, 0);
-
-	return PSCI_E_SUCCESS;
 }
 
 /*******************************************************************************
@@ -155,7 +178,7 @@
  * the highest affinity level which will be powered down. It performs the
  * actions common to the OFF and SUSPEND calls.
  ******************************************************************************/
-static int32_t juno_power_down_common(uint32_t afflvl)
+static void juno_power_down_common(uint32_t afflvl)
 {
 	uint32_t cluster_state = scpi_power_on;
 
@@ -176,8 +199,6 @@
 				 scpi_power_off,
 				 cluster_state,
 				 scpi_power_on);
-
-	return PSCI_E_SUCCESS;
 }
 
 /*******************************************************************************
@@ -191,13 +212,13 @@
  * global variables across calls. It will be wise to do flush a write to the
  * global to prevent unpredictable results.
  ******************************************************************************/
-static int32_t juno_affinst_off(uint32_t afflvl, uint32_t state)
+static void juno_affinst_off(uint32_t afflvl, uint32_t state)
 {
 	/* Determine if any platform actions need to be executed */
 	if (juno_do_plat_actions(afflvl, state) == -EAGAIN)
-		return PSCI_E_SUCCESS;
+		return;
 
-	return juno_power_down_common(afflvl);
+	juno_power_down_common(afflvl);
 }
 
 /*******************************************************************************
@@ -212,20 +233,20 @@
  * global variables across calls. It will be wise to do flush a write to the
  * global to prevent unpredictable results.
  ******************************************************************************/
-static int32_t juno_affinst_suspend(uint64_t sec_entrypoint,
+static void juno_affinst_suspend(uint64_t sec_entrypoint,
 				    uint32_t afflvl,
 				    uint32_t state)
 {
 	/* Determine if any platform actions need to be executed */
 	if (juno_do_plat_actions(afflvl, state) == -EAGAIN)
-		return PSCI_E_SUCCESS;
+		return;
 
 	/*
 	 * Setup mailbox with address for CPU entrypoint when it next powers up.
 	 */
 	juno_program_mailbox(read_mpidr_el1(), sec_entrypoint);
 
-	return juno_power_down_common(afflvl);
+	juno_power_down_common(afflvl);
 }
 
 /*******************************************************************************
@@ -235,10 +256,10 @@
  * TODO: At the moment we reuse the on finisher and reinitialize the secure
  * context. Need to implement a separate suspend finisher.
  ******************************************************************************/
-static int32_t juno_affinst_suspend_finish(uint32_t afflvl,
+static void juno_affinst_suspend_finish(uint32_t afflvl,
 					   uint32_t state)
 {
-	return juno_affinst_on_finish(afflvl, state);
+	juno_affinst_on_finish(afflvl, state);
 }
 
 /*******************************************************************************
@@ -279,21 +300,10 @@
 /*******************************************************************************
  * Handler called when an affinity instance is about to enter standby.
  ******************************************************************************/
-int32_t juno_affinst_standby(unsigned int power_state)
+void juno_affinst_standby(unsigned int power_state)
 {
-	unsigned int target_afflvl;
 	unsigned int scr;
 
-	/* Sanity check the requested state */
-	target_afflvl = psci_get_pstate_afflvl(power_state);
-
-	/*
-	 * It's possible to enter standby only on affinity level 0 i.e. a cpu
-	 * on the Juno. Ignore any other affinity level.
-	 */
-	if (target_afflvl != MPIDR_AFFLVL0)
-		return PSCI_E_INVALID_PARAMS;
-
 	scr = read_scr_el3();
 	/* Enable PhysicalIRQ bit for NS world to wake the CPU */
 	write_scr_el3(scr | SCR_IRQ_BIT);
@@ -306,8 +316,6 @@
 	 * done by eret while el3_exit to save some execution cycles.
 	 */
 	write_scr_el3(scr);
-
-	return PSCI_E_SUCCESS;
 }
 
 /*******************************************************************************
@@ -321,7 +329,8 @@
 	.affinst_suspend	= juno_affinst_suspend,
 	.affinst_suspend_finish	= juno_affinst_suspend_finish,
 	.system_off		= juno_system_off,
-	.system_reset		= juno_system_reset
+	.system_reset		= juno_system_reset,
+	.validate_power_state	= juno_validate_power_state
 };
 
 /*******************************************************************************