diff --git a/subsys/bluetooth/controller/ll_sw/ull_conn.c b/subsys/bluetooth/controller/ll_sw/ull_conn.c
index 60c8b324e0a..861efa5ba32 100644
--- a/subsys/bluetooth/controller/ll_sw/ull_conn.c
+++ b/subsys/bluetooth/controller/ll_sw/ull_conn.c
@@ -70,18 +70,6 @@
 #include "common/log.h"
 #include "hal/debug.h"
 
-/**
- *  User CPR Interval
- */
-#if !defined(CONFIG_BT_CTLR_USER_CPR_INTERVAL_MIN)
-/* Bluetooth defined CPR Interval Minimum (7.5ms) */
-#define CONN_INTERVAL_MIN(x) (6)
-#else /* CONFIG_BT_CTLR_USER_CPR_INTERVAL_MIN */
-/* Proprietary user defined CPR Interval Minimum */
-extern uint16_t ull_conn_interval_min_get(struct ll_conn *conn);
-#define CONN_INTERVAL_MIN(x) (MAX(ull_conn_interval_min_get(x), 1))
-#endif /* CONFIG_BT_CTLR_USER_CPR_INTERVAL_MIN */
-
 static int init_reset(void);
 #if !defined(CONFIG_BT_CTLR_LOW_LAT_ULL)
 static void tx_demux_sched(struct ll_conn *conn);
diff --git a/subsys/bluetooth/controller/ll_sw/ull_internal.h b/subsys/bluetooth/controller/ll_sw/ull_internal.h
index 7f1ed3cdd06..5acd6135cbb 100644
--- a/subsys/bluetooth/controller/ll_sw/ull_internal.h
+++ b/subsys/bluetooth/controller/ll_sw/ull_internal.h
@@ -4,6 +4,18 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+/**
+ *  User CPR Interval
+ */
+#if !defined(CONFIG_BT_CTLR_USER_CPR_INTERVAL_MIN)
+/* Bluetooth defined CPR Interval Minimum (7.5ms) */
+#define CONN_INTERVAL_MIN(x) (6)
+#else /* CONFIG_BT_CTLR_USER_CPR_INTERVAL_MIN */
+/* Proprietary user defined CPR Interval Minimum */
+extern uint16_t ull_conn_interval_min_get(struct ll_conn *conn);
+#define CONN_INTERVAL_MIN(x) (MAX(ull_conn_interval_min_get(x), 1))
+#endif /* CONFIG_BT_CTLR_USER_CPR_INTERVAL_MIN */
+
 /* Macro to convert time in us to connection interval units */
 #define RADIO_CONN_EVENTS(x, y) ((uint16_t)(((x) + (y) - 1) / (y)))
 
diff --git a/subsys/bluetooth/controller/ll_sw/ull_llcp_conn_upd.c b/subsys/bluetooth/controller/ll_sw/ull_llcp_conn_upd.c
index 3ec285bafd4..0ef65fe9738 100644
--- a/subsys/bluetooth/controller/ll_sw/ull_llcp_conn_upd.c
+++ b/subsys/bluetooth/controller/ll_sw/ull_llcp_conn_upd.c
@@ -42,10 +42,25 @@
 #include "hal/debug.h"
 
 /* Hardcoded instant delta +6 */
-#define CONN_UPDATE_INSTANT_DELTA 6U
+#define CONN_UPDATE_INSTANT_DELTA	6U
 
-/* TODO: Known, missing items (missing implementation):
- *	LL/CON/MAS/BV-34-C [Accepting Connection Parameter Request ? event masked]
+/* CPR parameter ranges */
+#define CONN_UPDATE_TIMEOUT_100MS	10U
+#define CONN_UPDATE_TIMEOUT_32SEC	3200U
+#define CONN_UPDATE_LATENCY_MAX		499U
+#define CONN_UPDATE_CONN_INTV_4SEC	3200U
+
+/*
+ * TODO - Known, missing items (missing implementation):
+ *
+ * If DLE procedure supported:
+ *  and current PHY is Coded PHY:
+ *  ... (5.3.6.B.5.1.1) the new connection interval shall be at least connIntervalCodedMin us.
+ *  ... (5.3.6.B.5.1.7.4) packet tx time restrictions should be in effect
+ *
+ * Inter-connection mutual exclusion on CPR
+ *
+ * LL/CON/MAS/BV-34-C [Accepting Connection Parameter Request w. event masked]
  */
 
 /* LLCP Local Procedure Connection Update FSM states */
@@ -55,6 +70,7 @@ enum {
 	LP_CU_STATE_WAIT_RX_CONN_PARAM_RSP,
 	LP_CU_STATE_WAIT_TX_CONN_UPDATE_IND,
 	LP_CU_STATE_WAIT_RX_CONN_UPDATE_IND,
+	LP_CU_STATE_WAIT_TX_REJECT_EXT_IND,
 	LP_CU_STATE_WAIT_INSTANT,
 	LP_CU_STATE_WAIT_NTF,
 };
@@ -139,6 +155,29 @@ static void cu_update_conn_parameters(struct ll_conn *conn, struct proc_ctx *ctx
 				   ctx->data.cu.instant);
 }
 
+#if defined(CONFIG_BT_CTLR_CONN_PARAM_REQ)
+static bool cu_check_conn_parameters(struct ll_conn *conn, struct proc_ctx *ctx)
+{
+	const uint16_t interval_min = ctx->data.cu.interval_min;
+	const uint16_t interval_max = ctx->data.cu.interval_max; /* unit conn events (ie 1.25ms) */
+	const uint16_t timeout = ctx->data.cu.timeout; /* unit 10ms */
+	const uint16_t latency = ctx->data.cu.latency;
+	const uint16_t preferred_periodicity = ctx->data.cu.preferred_periodicity;
+
+	/* Invalid parameters */
+	const bool invalid = ((interval_min < CONN_INTERVAL_MIN(conn)) ||
+	    (interval_max > CONN_UPDATE_CONN_INTV_4SEC) ||
+	    (interval_min > interval_max) ||
+	    (latency > CONN_UPDATE_LATENCY_MAX) ||
+	    (timeout < CONN_UPDATE_TIMEOUT_100MS) || (timeout > CONN_UPDATE_TIMEOUT_32SEC) ||
+	    ((timeout * 4U) <= /* *4U re. conn events is equivalent to *2U re. ms */
+	     ((latency + 1) * interval_max)) ||
+	    (preferred_periodicity > interval_max));
+
+	return !invalid;
+}
+#endif /* CONFIG_BT_CTLR_CONN_PARAM_REQ */
+
 static bool cu_should_notify_host(struct proc_ctx *ctx)
 {
 	return (((ctx->proc == PROC_CONN_PARAM_REQ) && (ctx->data.cu.error != 0U)) ||
@@ -162,6 +201,10 @@ static void lp_cu_tx(struct ll_conn *conn, struct proc_ctx *ctx, uint8_t opcode)
 	case PDU_DATA_LLCTRL_TYPE_CONN_PARAM_REQ:
 		llcp_pdu_encode_conn_param_req(ctx, pdu);
 		break;
+	case PDU_DATA_LLCTRL_TYPE_REJECT_EXT_IND:
+		llcp_pdu_encode_reject_ext_ind(pdu, PDU_DATA_LLCTRL_TYPE_CONN_PARAM_RSP,
+					       ctx->data.cu.error);
+		break;
 #endif /* CONFIG_BT_CTLR_CONN_PARAM_REQ */
 #if defined(CONFIG_BT_CENTRAL)
 	case PDU_DATA_LLCTRL_TYPE_CONN_UPDATE_IND:
@@ -214,6 +257,19 @@ static void lp_cu_complete(struct ll_conn *conn, struct proc_ctx *ctx, uint8_t e
 }
 
 #if defined(CONFIG_BT_CTLR_CONN_PARAM_REQ)
+static void lp_cu_send_reject_ext_ind(struct ll_conn *conn, struct proc_ctx *ctx, uint8_t evt,
+				      void *param)
+{
+	if (ctx->pause || !llcp_tx_alloc_peek(conn, ctx)) {
+		ctx->state = LP_CU_STATE_WAIT_TX_REJECT_EXT_IND;
+	} else {
+		llcp_rr_set_incompat(conn, INCOMPAT_NO_COLLISION);
+		lp_cu_tx(conn, ctx, PDU_DATA_LLCTRL_TYPE_REJECT_EXT_IND);
+		llcp_lr_complete(conn);
+		ctx->state = LP_CU_STATE_IDLE;
+	}
+}
+
 static void lp_cu_send_conn_param_req(struct ll_conn *conn, struct proc_ctx *ctx, uint8_t evt,
 				      void *param)
 {
@@ -304,6 +360,20 @@ static void lp_cu_st_idle(struct ll_conn *conn, struct proc_ctx *ctx, uint8_t ev
 }
 
 #if defined(CONFIG_BT_CTLR_CONN_PARAM_REQ)
+static void lp_cu_st_wait_tx_reject_ext_ind(struct ll_conn *conn, struct proc_ctx *ctx,
+					       uint8_t evt, void *param)
+{
+	switch (evt) {
+	case LP_CU_EVT_RUN:
+		lp_cu_send_reject_ext_ind(conn, ctx, evt, param);
+		break;
+	default:
+		/* Ignore other evts */
+		break;
+	}
+}
+
+
 static void lp_cu_st_wait_tx_conn_param_req(struct ll_conn *conn, struct proc_ctx *ctx, uint8_t evt,
 					    void *param)
 {
@@ -327,7 +397,14 @@ static void lp_cu_st_wait_rx_conn_param_rsp(struct ll_conn *conn, struct proc_ct
 
 	switch (evt) {
 	case LP_CU_EVT_CONN_PARAM_RSP:
+		llcp_pdu_decode_conn_param_rsp(ctx, param);
 		llcp_rr_set_incompat(conn, INCOMPAT_RESERVED);
+		/* Perform Param check and possibly reject (LL_REJECT_EXT_IND) */
+		if (!cu_check_conn_parameters(conn, ctx)) {
+			ctx->data.cu.error = BT_HCI_ERR_INVALID_LL_PARAM;
+			lp_cu_send_reject_ext_ind(conn, ctx, evt, param);
+			break;
+		}
 		lp_cu_send_conn_update_ind(conn, ctx, evt, param);
 		break;
 	case LP_CU_EVT_UNKNOWN:
@@ -407,10 +484,10 @@ static void lp_cu_check_instant(struct ll_conn *conn, struct proc_ctx *ctx, uint
 		/* Procedure is complete when the instant has passed, and the
 		 * new connection event parameters have been applied.
 		 */
+		llcp_rr_set_incompat(conn, INCOMPAT_NO_COLLISION);
 		cu_update_conn_parameters(conn, ctx);
 		notify = cu_should_notify_host(ctx);
 		if (notify) {
-			llcp_rr_set_incompat(conn, INCOMPAT_NO_COLLISION);
 			ctx->data.cu.error = BT_HCI_ERR_SUCCESS;
 			lp_cu_complete(conn, ctx, evt, param);
 		} else {
@@ -471,6 +548,11 @@ static void lp_cu_execute_fsm(struct ll_conn *conn, struct proc_ctx *ctx, uint8_
 		lp_cu_st_wait_rx_conn_update_ind(conn, ctx, evt, param);
 		break;
 #endif /* CONFIG_BT_PERIPHERAL */
+#if defined(CONFIG_BT_CTLR_CONN_PARAM_REQ)
+	case LP_CU_STATE_WAIT_TX_REJECT_EXT_IND:
+		lp_cu_st_wait_tx_reject_ext_ind(conn, ctx, evt, param);
+		break;
+#endif /* CONFIG_BT_CTLR_CONN_PARAM_REQ */
 	case LP_CU_STATE_WAIT_INSTANT:
 		lp_cu_st_wait_instant(conn, ctx, evt, param);
 		break;
@@ -719,7 +801,14 @@ static void rp_cu_st_wait_rx_conn_param_req(struct ll_conn *conn, struct proc_ct
 	case RP_CU_EVT_CONN_PARAM_REQ:
 		llcp_pdu_decode_conn_param_req(ctx, param);
 
-		bool params_changed =
+		/* Perform Param check and reject if invalid (LL_REJECT_EXT_IND) */
+		if (!cu_check_conn_parameters(conn, ctx)) {
+			ctx->data.cu.error = BT_HCI_ERR_INVALID_LL_PARAM;
+			rp_cu_send_reject_ext_ind(conn, ctx, evt, param);
+			break;
+		}
+
+		const bool params_changed =
 			cu_have_params_changed(conn, ctx->data.cu.interval_max,
 					       ctx->data.cu.latency, ctx->data.cu.timeout);
 
diff --git a/tests/bluetooth/controller/ctrl_conn_update/src/main.c b/tests/bluetooth/controller/ctrl_conn_update/src/main.c
index 5945cf9efd3..6990e6bf255 100644
--- a/tests/bluetooth/controller/ctrl_conn_update/src/main.c
+++ b/tests/bluetooth/controller/ctrl_conn_update/src/main.c
@@ -80,6 +80,32 @@ struct pdu_data_llctrl_conn_param_rsp conn_param_rsp = { .interval_min = INTVL_M
 							 .offset4 = 0xffffU,
 							 .offset5 = 0xffffU };
 
+/* Invalid conn_param_req PDU */
+struct pdu_data_llctrl_conn_param_req conn_param_req_invalid = { .interval_min = INTVL_MIN - 1,
+							 .interval_max = INTVL_MAX + 1,
+							 .latency = LATENCY,
+							 .timeout = TIMEOUT - 1,
+							 .preferred_periodicity = 0U,
+							 .reference_conn_event_count = 0u,
+							 .offset0 = 0x0000U,
+							 .offset1 = 0xffffU,
+							 .offset2 = 0xffffU,
+							 .offset3 = 0xffffU,
+							 .offset4 = 0xffffU,
+							 .offset5 = 0xffffU };
+/* Invalid conn_param_rsp PDU */
+struct pdu_data_llctrl_conn_param_rsp conn_param_rsp_invalid = { .interval_min = INTVL_MIN - 1,
+								 .interval_max = INTVL_MAX + 1,
+								 .latency = LATENCY,
+								 .timeout = TIMEOUT - 1,
+								 .preferred_periodicity = 0U,
+								 .reference_conn_event_count = 0u,
+								 .offset0 = 0x0000U,
+								 .offset1 = 0xffffU,
+								 .offset2 = 0xffffU,
+								 .offset3 = 0xffffU,
+								 .offset4 = 0xffffU,
+								 .offset5 = 0xffffU };
 /* Different PDU contents for (B) */
 
 /* Default conn_param_req PDU (B) */
@@ -169,7 +195,7 @@ static bool is_instant_reached(struct ll_conn *conn, uint16_t instant)
  * Central requests change in LE connection parameters, peripheral’s Host accepts.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_M  |                    | LT  |
+ * | UT  |                    | LL_C  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    | LE Connection Update      |                           |
@@ -278,12 +304,85 @@ void test_conn_update_central_loc_accept(void)
 		      "Free CTX buffers %d", ctx_buffers_free());
 }
 
+/*
+ * Central-initiated Connection Parameters Request procedure.
+ * Central requests change in LE connection parameters, peripheral
+ * responds with invalid params
+ *
+ * +-----+                    +-------+                    +-----+
+ * | UT  |                    | LL_C  |                    | LT  |
+ * +-----+                    +-------+                    +-----+
+ *    |                           |                           |
+ *    | LE Connection Update      |                           |
+ *    |-------------------------->|                           |
+ *    |                           | LL_CONNECTION_PARAM_REQ   |
+ *    |                           |-------------------------->|
+ *    |                           |                           |
+ *    |                           |   LL_CONNECTION_PARAM_RSP |
+ *    |                           |<--------------------------|
+ *    |                           |                           |
+ *    |                           | LL_REJECT_EXT_IND         |
+ *    |                           |-------------------------->|
+ *    |                           |                           |
+ *    |                           |                           |
+ *    |                           |                           |
+ */
+void test_conn_update_central_loc_invalid_param_rsp(void)
+{
+	uint8_t err;
+	struct node_tx *tx;
+	struct pdu_data_llctrl_reject_ext_ind reject_ext_ind = {
+		.reject_opcode = PDU_DATA_LLCTRL_TYPE_CONN_PARAM_RSP,
+		.error_code = BT_HCI_ERR_INVALID_LL_PARAM
+	};
+
+
+	/* Role */
+	test_set_role(&conn, BT_HCI_ROLE_CENTRAL);
+
+	/* Connect */
+	ull_cp_state_set(&conn, ULL_CP_CONNECTED);
+
+	/* Initiate a Connection Parameter Request Procedure */
+	err = ull_cp_conn_update(&conn, INTVL_MIN, INTVL_MAX, LATENCY, TIMEOUT);
+	zassert_equal(err, BT_HCI_ERR_SUCCESS, NULL);
+
+	/* Prepare */
+	event_prepare(&conn);
+
+	/* Tx Queue should have one LL Control PDU */
+	lt_rx(LL_CONNECTION_PARAM_REQ, &conn, &tx, &conn_param_req);
+	lt_rx_q_is_empty(&conn);
+
+	/* Rx */
+	lt_tx(LL_CONNECTION_PARAM_RSP, &conn, &conn_param_rsp_invalid);
+
+	/* Done */
+	event_done(&conn);
+
+	/* Release Tx */
+	ull_cp_release_tx(&conn, tx);
+
+	/* Prepare */
+	event_prepare(&conn);
+
+	/* Tx Queue should have one LL Control PDU */
+	lt_rx(LL_REJECT_EXT_IND, &conn, &tx, &reject_ext_ind);
+	lt_rx_q_is_empty(&conn);
+
+	/* Done */
+	event_done(&conn);
+
+	zassert_equal(ctx_buffers_free(), test_ctx_buffers_cnt(),
+		      "Free CTX buffers %d", ctx_buffers_free());
+}
+
 /*
  * Central-initiated Connection Parameters Request procedure.
  * Central requests change in LE connection parameters, peripheral’s Host rejects.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_M  |                    | LT  |
+ * | UT  |                    | LL_C  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    | LE Connection Update      |                           |
@@ -353,7 +452,7 @@ void test_conn_update_central_loc_reject(void)
  * Central requests change in LE connection parameters, peripheral’s Host is legacy.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_M  |                    | LT  |
+ * | UT  |                    | LL_C  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    | LE Connection Update      |                           |
@@ -477,7 +576,7 @@ void test_conn_update_central_loc_remote_legacy(void)
  * support Connection Parameters Request procedure, features not exchanged.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_M  |                    | LT  |
+ * | UT  |                    | LL_C  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    | LE Connection Update      |                           |
@@ -600,7 +699,7 @@ void test_conn_update_central_loc_unsupp_wo_feat_exch(void)
  * support Connection Parameters Request procedure, features exchanged.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_M  |                    | LT  |
+ * | UT  |                    | LL_C  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    | LE Connection Update      |                           |
@@ -705,7 +804,7 @@ void test_conn_update_central_loc_unsupp_w_feat_exch(void)
  * Procedure collides and is rejected.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_M  |                    | LT  |
+ * | UT  |                    | LL_C  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    | LE Connection Update      |                           |
@@ -863,7 +962,7 @@ void test_conn_update_central_loc_collision(void)
  * Peripheral requests change in LE connection parameters, central’s Host accepts.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_M  |                    | LT  |
+ * | UT  |                    | LL_C  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    |                           |   LL_CONNECTION_PARAM_REQ |
@@ -978,12 +1077,69 @@ void test_conn_update_central_rem_accept(void)
 		      "Free CTX buffers %d", ctx_buffers_free());
 }
 
+/*
+ * Peripheral-initiated Connection Parameters Request procedure.
+ * Peripheral requests change in LE connection with invalid parameters,
+ *
+ * +-----+                    +-------+                    +-----+
+ * | UT  |                    | LL_C  |                    | LT  |
+ * +-----+                    +-------+                    +-----+
+ *    |                           |                           |
+ *    |                           |   LL_CONNECTION_PARAM_REQ |
+ *    |                           |<--------------------------|
+ *    |                           |                           |
+ *    |                           |                           |
+ *    |                           | LL_REJECT_EXT_IND         |
+ *    |                           |-------------------------->|
+ *    |                           |                           |
+ *    |                           |                           |
+ */
+void test_conn_update_central_rem_invalid_req(void)
+{
+	struct node_tx *tx;
+	struct pdu_data_llctrl_reject_ext_ind reject_ext_ind = {
+		.reject_opcode = PDU_DATA_LLCTRL_TYPE_CONN_PARAM_REQ,
+		.error_code = BT_HCI_ERR_INVALID_LL_PARAM
+	};
+
+	/* Role */
+	test_set_role(&conn, BT_HCI_ROLE_CENTRAL);
+
+	/* Connect */
+	ull_cp_state_set(&conn, ULL_CP_CONNECTED);
+
+	/* Prepare */
+	event_prepare(&conn);
+
+	/* Rx */
+	lt_tx(LL_CONNECTION_PARAM_REQ, &conn, &conn_param_req_invalid);
+
+	/* Done */
+	event_done(&conn);
+
+	/* Prepare */
+	event_prepare(&conn);
+
+	/* Tx Queue should have one LL Control PDU */
+	lt_rx(LL_REJECT_EXT_IND, &conn, &tx, &reject_ext_ind);
+	lt_rx_q_is_empty(&conn);
+
+	/* Done */
+	event_done(&conn);
+
+	/* Release Tx */
+	ull_cp_release_tx(&conn, tx);
+	zassert_equal(ctx_buffers_free(), test_ctx_buffers_cnt(),
+		      "Free CTX buffers %d", ctx_buffers_free());
+
+}
+
 /*
  * Peripheral-initiated Connection Parameters Request procedure.
  * Peripheral requests change in LE connection parameters, central’s Host rejects.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_M  |                    | LT  |
+ * | UT  |                    | LL_C  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    |                           |   LL_CONNECTION_PARAM_REQ |
@@ -1060,7 +1216,7 @@ void test_conn_update_central_rem_reject(void)
  * support Connection Parameters Request procedure.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_M  |                    | LT  |
+ * | UT  |                    | LL_C  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    |                           |   LL_CONNECTION_PARAM_REQ |
@@ -1094,7 +1250,7 @@ void test_conn_update_central_rem_unsupp_feat(void)
  * Central-initiated Connection Parameters Request procedure is resumed.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_M  |                    | LT  |
+ * | UT  |                    | LL_C  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    |                           |   LL_CONNECTION_PARAM_REQ |
@@ -1323,7 +1479,7 @@ void test_conn_update_central_rem_collision(void)
  * Peripheral requests change in LE connection parameters, central’s Host accepts.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_S  |                    | LT  |
+ * | UT  |                    | LL_P  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    | LE Connection Update      |                           |
@@ -1425,7 +1581,7 @@ void test_conn_update_periph_loc_accept(void)
  * Peripheral requests change in LE connection parameters, central’s Host rejects.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_S  |                    | LT  |
+ * | UT  |                    | LL_P  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    | LE Connection Update      |                           |
@@ -1505,7 +1661,7 @@ void test_conn_update_periph_loc_reject(void)
  * support Connection Parameters Request procedure, features not exchanged.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_S  |                    | LT  |
+ * | UT  |                    | LL_P  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    | LE Connection Update      |                           |
@@ -1584,7 +1740,7 @@ void test_conn_update_periph_loc_unsupp_feat_wo_feat_exch(void)
  * support Connection Parameters Request procedure, features exchanged.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_S  |                    | LT  |
+ * | UT  |                    | LL_P  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    | LE Connection Update      |                           |
@@ -1638,7 +1794,7 @@ void test_conn_update_periph_loc_unsupp_feat_w_feat_exch(void)
  * Central requests change in LE connection parameters, peripheral’s Host accepts.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_S  |                    | LT  |
+ * | UT  |                    | LL_P  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    | LE Connection Update      |                           |
@@ -1809,7 +1965,7 @@ void test_conn_update_periph_loc_collision(void)
  * Central requests change in LE connection parameters, peripheral’s Host accepts.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_S  |                    | LT  |
+ * | UT  |                    | LL_P  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    |                           |   LL_CONNECTION_PARAM_REQ |
@@ -1934,12 +2090,69 @@ void test_conn_update_periph_rem_accept(void)
 		      "Free CTX buffers %d", ctx_buffers_free());
 }
 
+/*
+ * Central-initiated Connection Parameters Request procedure.
+ * Central requests change in LE connection with invalid parameters,
+ *
+ * +-----+                    +-------+                    +-----+
+ * | UT  |                    | LL_P  |                    | LT  |
+ * +-----+                    +-------+                    +-----+
+ *    |                           |                           |
+ *    |                           |   LL_CONNECTION_PARAM_REQ |
+ *    |                           |<--------------------------|
+ *    |                           |                           |
+ *    |                           |                           |
+ *    |                           | LL_REJECT_EXT_IND         |
+ *    |                           |-------------------------->|
+ *    |                           |                           |
+ *    |                           |                           |
+ */
+void test_conn_update_periph_rem_invalid_req(void)
+{
+	struct node_tx *tx;
+	struct pdu_data_llctrl_reject_ext_ind reject_ext_ind = {
+		.reject_opcode = PDU_DATA_LLCTRL_TYPE_CONN_PARAM_REQ,
+		.error_code = BT_HCI_ERR_INVALID_LL_PARAM
+	};
+
+	/* Role */
+	test_set_role(&conn, BT_HCI_ROLE_PERIPHERAL);
+
+	/* Connect */
+	ull_cp_state_set(&conn, ULL_CP_CONNECTED);
+
+	/* Prepare */
+	event_prepare(&conn);
+
+	/* Rx */
+	lt_tx(LL_CONNECTION_PARAM_REQ, &conn, &conn_param_req_invalid);
+
+	/* Done */
+	event_done(&conn);
+
+	/* Prepare */
+	event_prepare(&conn);
+
+	/* Tx Queue should have one LL Control PDU */
+	lt_rx(LL_REJECT_EXT_IND, &conn, &tx, &reject_ext_ind);
+	lt_rx_q_is_empty(&conn);
+
+	/* Done */
+	event_done(&conn);
+
+	/* Release Tx */
+	ull_cp_release_tx(&conn, tx);
+	zassert_equal(ctx_buffers_free(), test_ctx_buffers_cnt(),
+		      "Free CTX buffers %d", ctx_buffers_free());
+
+}
+
 /*
  * Central-initiated Connection Parameters Request procedure.
  * Central requests change in LE connection parameters, peripheral’s Host rejects.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_S  |                    | LT  |
+ * | UT  |                    | LL_P  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    |                           |   LL_CONNECTION_PARAM_REQ |
@@ -2020,7 +2233,7 @@ void test_conn_update_periph_rem_reject(void)
  * support Connection Parameters Request procedure.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_S  |                    | LT  |
+ * | UT  |                    | LL_P  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    |                           |   LL_CONNECTION_PARAM_REQ |
@@ -2054,7 +2267,7 @@ void test_conn_update_periph_rem_unsupp_feat(void)
  * Peripheral-initiated Connection Parameters Request procedure is resumed.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_S  |                    | LT  |
+ * | UT  |                    | LL_P  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    |                           |   LL_CONNECTION_PARAM_REQ |
@@ -2272,7 +2485,7 @@ void test_conn_update_periph_rem_collision(void)
  * Central requests update of LE connection.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_M  |                    | LT  |
+ * | UT  |                    | LL_C  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    | LE Connection Update      |                           |
@@ -2383,7 +2596,7 @@ void test_conn_update_central_loc_accept_no_param_req(void)
  * Central receives Connection Update parameters.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_M  |                    | LT  |
+ * | UT  |                    | LL_C  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    |                           |  LL_CONNECTION_UPDATE_IND |
@@ -2440,7 +2653,7 @@ void test_conn_update_central_rem_accept_no_param_req(void)
  * Peripheral receives Connection Update parameters.
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_S  |                    | LT  |
+ * | UT  |                    | LL_P  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    |                           |  LL_CONNECTION_UPDATE_IND |
@@ -2530,7 +2743,7 @@ void test_conn_update_periph_rem_accept_no_param_req(void)
  * Peripheral-initiated Connection Update procedure (not allowed).
  *
  * +-----+                    +-------+                    +-----+
- * | UT  |                    | LL_S  |                    | LT  |
+ * | UT  |                    | LL_P  |                    | LT  |
  * +-----+                    +-------+                    +-----+
  *    |                           |                           |
  *    | LE Connection Update      |                           |
@@ -2577,6 +2790,8 @@ void test_main(void)
 		central_loc,
 		ztest_unit_test_setup_teardown(test_conn_update_central_loc_accept,
 					       setup, unit_test_noop),
+		ztest_unit_test_setup_teardown(test_conn_update_central_loc_invalid_param_rsp,
+					       setup, unit_test_noop),
 		ztest_unit_test_setup_teardown(test_conn_update_central_loc_reject,
 					       setup, unit_test_noop),
 		ztest_unit_test_setup_teardown(test_conn_update_central_loc_remote_legacy,
@@ -2591,6 +2806,8 @@ void test_main(void)
 	ztest_test_suite(central_rem,
 			 ztest_unit_test_setup_teardown(test_conn_update_central_rem_accept,
 							setup, unit_test_noop),
+			 ztest_unit_test_setup_teardown(test_conn_update_central_rem_invalid_req,
+							setup, unit_test_noop),
 			 ztest_unit_test_setup_teardown(test_conn_update_central_rem_reject,
 							setup, unit_test_noop),
 			 ztest_unit_test_setup_teardown(test_conn_update_central_rem_unsupp_feat,
@@ -2614,6 +2831,8 @@ void test_main(void)
 	ztest_test_suite(periph_rem,
 			 ztest_unit_test_setup_teardown(test_conn_update_periph_rem_accept,
 							setup, unit_test_noop),
+			 ztest_unit_test_setup_teardown(test_conn_update_periph_rem_invalid_req,
+							setup, unit_test_noop),
 			 ztest_unit_test_setup_teardown(test_conn_update_periph_rem_reject,
 							setup, unit_test_noop),
 			 ztest_unit_test_setup_teardown(test_conn_update_periph_rem_unsupp_feat,