diff --git a/test/gatt_client/Makefile b/test/gatt_client/Makefile
index 60d459652..0de720a68 100644
--- a/test/gatt_client/Makefile
+++ b/test/gatt_client/Makefile
@@ -5,7 +5,7 @@ CC = g++
 BTSTACK_ROOT =  ../..
 
 CFLAGS  = -DUNIT_TEST -x c++ -g -Wall -Wnarrowing -Wconversion-null -I. -I../ -I${BTSTACK_ROOT}/src
-CFLAGS += -fprofile-arcs -ftest-coverage
+CFLAGS += -fprofile-arcs -ftest-coverage -fsanitize=address
 LDFLAGS +=  -lCppUTest -lCppUTestExt
 
 VPATH += ${BTSTACK_ROOT}/src
diff --git a/test/gatt_client/mock.c b/test/gatt_client/mock.c
index a90161517..bdfa0e9c8 100644
--- a/test/gatt_client/mock.c
+++ b/test/gatt_client/mock.c
@@ -11,12 +11,14 @@
 #include "ble/gatt_client.h"
 #include "ble/sm.h"
 
+#define PREBUFFER_SIZE (HCI_INCOMING_PRE_BUFFER_SIZE + 8)
+
 static btstack_packet_handler_t att_packet_handler;
 static void (*registered_hci_event_handler) (uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size) = NULL;
 
 static btstack_linked_list_t     connections;
 static const uint16_t max_mtu = 23;
-static uint8_t  l2cap_stack_buffer[HCI_INCOMING_PRE_BUFFER_SIZE + 8 + max_mtu];	// pre buffer + HCI Header + L2CAP header
+static uint8_t  l2cap_stack_buffer[PREBUFFER_SIZE + max_mtu];	// pre buffer + HCI Header + L2CAP header
 static uint16_t gatt_client_handle = 0x40;
 static hci_connection_t hci_connection;
 
@@ -76,8 +78,7 @@ int  l2cap_can_send_connectionless_packet_now(void){
 }
 
 uint8_t *l2cap_get_outgoing_buffer(void){
-	// printf("l2cap_get_outgoing_buffer\n");
-	return (uint8_t *)&l2cap_stack_buffer; // 8 bytes
+	return (uint8_t *)&l2cap_stack_buffer[HCI_INCOMING_PRE_BUFFER_SIZE + 8];
 }
 
 uint16_t l2cap_max_mtu(void){
@@ -116,8 +117,9 @@ void l2cap_request_can_send_fix_channel_now_event(uint16_t handle, uint16_t chan
 int l2cap_send_prepared_connectionless(uint16_t handle, uint16_t cid, uint16_t len){
 	att_connection_t att_connection;
 	att_init_connection(&att_connection);
-	uint8_t response[max_mtu];
-	uint16_t response_len = att_handle_request(&att_connection, l2cap_get_outgoing_buffer(), len, &response[0]);
+	uint8_t response_buffer[PREBUFFER_SIZE + max_mtu];
+	uint8_t * response = &response_buffer[PREBUFFER_SIZE];
+	uint16_t response_len = att_handle_request(&att_connection, l2cap_get_outgoing_buffer(), len, response);
 	if (response_len){
 		att_packet_handler(ATT_DATA_PACKET, gatt_client_handle, &response[0], response_len);
 	}