diff --git a/src/btstack_crypto.c b/src/btstack_crypto.c
index 2f949dd99..f1f6f2ef1 100644
--- a/src/btstack_crypto.c
+++ b/src/btstack_crypto.c
@@ -1160,8 +1160,11 @@ static void btstack_crypto_event_handler(uint8_t packet_type, uint16_t cid, uint
                     btstack_crypto_wait_for_hci_result = 0;
                     if (hci_subevent_le_generate_dhkey_complete_get_status(packet)){
                         log_error("Generate DHKEY failed -> abort");
+                        // set DHKEY to 0xff..ff
+                        memset(btstack_crypto_ec_p192->dhkey, 0xff, 32);
+                    } else {
+                        hci_subevent_le_generate_dhkey_complete_get_dhkey(packet, btstack_crypto_ec_p192->dhkey);
                     }
-                    hci_subevent_le_generate_dhkey_complete_get_dhkey(packet, btstack_crypto_ec_p192->dhkey);
                     // done
                     btstack_linked_list_pop(&btstack_crypto_operations);
                     (*btstack_crypto_ec_p192->btstack_crypto.context_callback.callback)(btstack_crypto_ec_p192->btstack_crypto.context_callback.context);                    
diff --git a/src/btstack_crypto.h b/src/btstack_crypto.h
index 3d1065876..20b445449 100644
--- a/src/btstack_crypto.h
+++ b/src/btstack_crypto.h
@@ -206,6 +206,8 @@ void btstack_crypto_ecc_p256_generate_key(btstack_crypto_ecc_p256_t * request, u
 
 /**
  * Calculate Diffie-Hellman Key based on local private key and remote public key
+ * @note Bluetooth Core v5.1+ requires the Controller to return an error if the public key is invalid
+ *       In this case, dhkey will be set to 0xff..ff
  * @param request
  * @param public_key (64 bytes)
  * @param dhkey (32 bytes)
@@ -215,7 +217,8 @@ void btstack_crypto_ecc_p256_generate_key(btstack_crypto_ecc_p256_t * request, u
 void btstack_crypto_ecc_p256_calculate_dhkey(btstack_crypto_ecc_p256_t * request, const uint8_t * public_key, uint8_t * dhkey, void (* callback)(void * arg), void * callback_arg);
 
 /*
- * Validate public key (not implemented for LE Controller ECC)
+ * Validate public key
+ * @note Not implemented for ECC in Controller. @see btstack_crypto_ecc_p256_calculate_dhkey
  * @param public_key (64 bytes)
  * @result 0 == valid
  */