diff --git a/core/hmi.c b/core/hmi.c
index d97f3fc03384..709f16bd0bdc 100644
--- a/core/hmi.c
+++ b/core/hmi.c
@@ -288,7 +288,7 @@ static int setup_scom_addresses(void)
 
 static int queue_hmi_event(struct OpalHMIEvent *hmi_evt, int recover, uint64_t *out_flags)
 {
-	size_t num_params;
+	size_t size;
 
 	/* Don't queue up event if recover == -1 */
 	if (recover == -1)
@@ -307,13 +307,13 @@ static int queue_hmi_event(struct OpalHMIEvent *hmi_evt, int recover, uint64_t *
 	 * num_params divide the struct size by 8 bytes to get exact
 	 * num_params value.
 	 */
-	num_params = ALIGN_UP(sizeof(*hmi_evt), sizeof(u64)) / sizeof(u64);
+	size = ALIGN_UP(sizeof(*hmi_evt), sizeof(u64));
 
 	*out_flags |= OPAL_HMI_FLAGS_NEW_EVENT;
 
 	/* queue up for delivery to host. */
 	return _opal_queue_msg(OPAL_MSG_HMI_EVT, NULL, NULL,
-				num_params, (uint64_t *)hmi_evt);
+				size, hmi_evt);
 }
 
 static int read_core_fir(uint32_t chip_id, uint32_t core_id, uint64_t *core_fir)
diff --git a/core/opal-msg.c b/core/opal-msg.c
index d3dd2ae3cb6f..907a9e0af340 100644
--- a/core/opal-msg.c
+++ b/core/opal-msg.c
@@ -36,7 +36,7 @@ static struct lock opal_msg_lock = LOCK_UNLOCKED;
 
 int _opal_queue_msg(enum opal_msg_type msg_type, void *data,
 		    void (*consumed)(void *data, int status),
-		    size_t num_params, const u64 *params)
+		    size_t params_size, const void *params)
 {
 	struct opal_msg_entry *entry;
 
@@ -57,11 +57,11 @@ int _opal_queue_msg(enum opal_msg_type msg_type, void *data,
 	entry->data = data;
 	entry->msg.msg_type = cpu_to_be32(msg_type);
 
-	if (num_params > ARRAY_SIZE(entry->msg.params)) {
+	if (params_size > OPAL_MSG_FIXED_PARAMS_SIZE) {
 		prerror("Discarding extra parameters\n");
-		num_params = ARRAY_SIZE(entry->msg.params);
+		params_size = OPAL_MSG_FIXED_PARAMS_SIZE;
 	}
-	memcpy(entry->msg.params, params, num_params*sizeof(u64));
+	memcpy(entry->msg.params, params, params_size);
 
 	list_add_tail(&msg_pending_list, &entry->link);
 	opal_update_pending_evt(OPAL_EVENT_MSG_PENDING,
diff --git a/hw/occ.c b/hw/occ.c
index d0ff4de96104..4e9783934a62 100644
--- a/hw/occ.c
+++ b/hw/occ.c
@@ -908,8 +908,9 @@ static void occ_throttle_poll(void *data __unused)
 			occ_msg.type = cpu_to_be64(OCC_THROTTLE);
 			occ_msg.chip = 0;
 			occ_msg.throttle_status = 0;
-			rc = _opal_queue_msg(OPAL_MSG_OCC, NULL, NULL, 3,
-					     (uint64_t *)&occ_msg);
+			rc = _opal_queue_msg(OPAL_MSG_OCC, NULL, NULL,
+					     sizeof(struct opal_occ_msg),
+					     &occ_msg);
 			if (!rc)
 				occ_reset = false;
 		}
@@ -929,7 +930,8 @@ static void occ_throttle_poll(void *data __unused)
 				occ_msg.throttle_status = cpu_to_be64(throttle);
 				rc = _opal_queue_msg(OPAL_MSG_OCC, NULL,
 						     occ_msg_consumed,
-						     3, (uint64_t *)&occ_msg);
+						     sizeof(struct opal_occ_msg),
+						     &occ_msg);
 				if (!rc) {
 					chip->throttle = throttle;
 					occ_opal_msg_outstanding = true;
@@ -1938,8 +1940,8 @@ static void __occ_do_load(u8 scope, u32 dbob_id __unused, u32 seq_id)
 	} else if (!rc) {
 		struct opal_occ_msg occ_msg = { CPU_TO_BE64(OCC_LOAD), 0, 0 };
 
-		rc = _opal_queue_msg(OPAL_MSG_OCC, NULL, NULL, 3,
-				     (uint64_t *)&occ_msg);
+		rc = _opal_queue_msg(OPAL_MSG_OCC, NULL, NULL,
+				     sizeof(struct opal_occ_msg), &occ_msg);
 		if (rc)
 			prlog(PR_INFO, "OCC: Failed to queue message %d\n",
 			      OCC_LOAD);
@@ -2062,8 +2064,8 @@ int occ_msg_queue_occ_reset(void)
 	int rc;
 
 	lock(&occ_lock);
-	rc = _opal_queue_msg(OPAL_MSG_OCC, NULL, NULL, 3,
-			     (uint64_t *)&occ_msg);
+	rc = _opal_queue_msg(OPAL_MSG_OCC, NULL, NULL,
+			     sizeof(struct opal_occ_msg), &occ_msg);
 	if (rc) {
 		prlog(PR_INFO, "OCC: Failed to queue OCC_RESET message\n");
 		goto out;
diff --git a/hw/prd.c b/hw/prd.c
index da24475443d5..9992aecf5186 100644
--- a/hw/prd.c
+++ b/hw/prd.c
@@ -212,8 +212,8 @@ static void send_next_pending_event(void)
 	 * disabled then we shouldn't propagate PRD events to the host.
 	 */
 	if (prd_enabled)
-		_opal_queue_msg(OPAL_MSG_PRD, prd_msg, prd_msg_consumed, 4,
-				(uint64_t *)prd_msg);
+		_opal_queue_msg(OPAL_MSG_PRD, prd_msg, prd_msg_consumed,
+				prd_msg->hdr.size, prd_msg);
 }
 
 static void __prd_event(uint32_t proc, uint8_t event)
@@ -421,8 +421,8 @@ static int prd_msg_handle_firmware_req(struct opal_prd_msg *msg)
 	}
 
 	if (!rc)
-		rc = _opal_queue_msg(OPAL_MSG_PRD, prd_msg, prd_msg_consumed, 4,
-				(uint64_t *) prd_msg);
+		rc = _opal_queue_msg(OPAL_MSG_PRD, prd_msg, prd_msg_consumed,
+				     prd_msg->hdr.size, prd_msg);
 	else
 		prd_msg_inuse = false;
 
diff --git a/include/opal-msg.h b/include/opal-msg.h
index 9be70334dc55..bfe148be65a5 100644
--- a/include/opal-msg.h
+++ b/include/opal-msg.h
@@ -30,13 +30,18 @@
 /* Max size of struct opal_msg */
 #define OPAL_MSG_SIZE		(64 * 1024)
 
+/* opal_msg fixed parameters size */
+#define OPAL_MSG_HDR_SIZE		(offsetof(struct opal_msg, params))
+#define OPAL_MSG_FIXED_PARAMS_SIZE	\
+				(sizeof(struct opal_msg) - OPAL_MSG_HDR_SIZE)
+
 int _opal_queue_msg(enum opal_msg_type msg_type, void *data,
 		    void (*consumed)(void *data, int status),
-		    size_t num_params, const u64 *params);
+		    size_t params_size, const void *params);
 
 #define opal_queue_msg(msg_type, data, cb, ...) \
 	_opal_queue_msg(msg_type, data, cb, \
-			sizeof((u64[]) {__VA_ARGS__})/sizeof(u64), \
+			sizeof((u64[]) {__VA_ARGS__}), \
 			(u64[]) {__VA_ARGS__});
 
 void opal_init_msg(void);