diff --git a/pkg/wakaama/contrib/objects/device.c b/pkg/wakaama/contrib/objects/device.c
index 2ccfdc6cf1..1ecf4c0fa4 100644
--- a/pkg/wakaama/contrib/objects/device.c
+++ b/pkg/wakaama/contrib/objects/device.c
@@ -20,6 +20,7 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "kernel_defines.h"
 #include "liblwm2m.h"
 #include "objects/device.h"
 #include "lwm2m_client_config.h"
@@ -77,7 +78,7 @@ static uint8_t prv_device_discover(uint16_t instance_id, int *num_dataP,
             LWM2M_RES_BINDINGS, LWM2M_RES_TYPE, LWM2M_RES_HW_VERSION,
             LWM2M_RES_SW_VERSION,
         };
-        int len = sizeof(res) / sizeof(uint16_t);
+        int len = ARRAY_SIZE(res);
 
         *data_arrayP = lwm2m_data_new(len);
         if (*data_arrayP == NULL) {
@@ -136,7 +137,7 @@ static uint8_t prv_device_read(uint16_t instance_id, int *num_dataP,
             LWM2M_RES_FW_VER,       LWM2M_RES_HW_VERSION, LWM2M_RES_SW_VERSION,
             LWM2M_RES_BINDINGS,     LWM2M_RES_TYPE,       LWM2M_RES_ERROR_CODE,
         };
-        int cnt = sizeof(resList) / sizeof(uint16_t);
+        int cnt = ARRAY_SIZE(resList);
         *data_arrayP = lwm2m_data_new(cnt);
         if (*data_arrayP == NULL) {
             result = COAP_500_INTERNAL_SERVER_ERROR;