diff --git a/features/FEATURE_BLE/targets/TARGET_NORDIC/TARGET_NRF51/source/nRF5xGattServer.h b/features/FEATURE_BLE/targets/TARGET_NORDIC/TARGET_NRF51/source/nRF5xGattServer.h
index ca4e069d80..6be90ff733 100644
--- a/features/FEATURE_BLE/targets/TARGET_NORDIC/TARGET_NRF51/source/nRF5xGattServer.h
+++ b/features/FEATURE_BLE/targets/TARGET_NORDIC/TARGET_NRF51/source/nRF5xGattServer.h
@@ -39,7 +39,7 @@ public:
 
     /* nRF51 Functions */
     void eventCallback(void);
-    void hwCallback(ble_evt_t *p_ble_evt);
+    void hwCallback(const ble_evt_t *p_ble_evt);
 
 
 private: