diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4499d432d..ec4e3f5cd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -42,6 +42,7 @@ SPDX-License-Identifier: GPL-3.0-or-later
 - irc: display a warning for each unknown or invalid server option in commands /connect and /server
 - relay/api: fix crash when an invalid HTTP request is received from a client
 - relay/api: return HTTP error 404 instead of 400 when the buffer is not found in resources completion and input
+- relay/api: return HTTP error 400 in case of invalid body in resource ping
 
 ## Version 4.7.1 (2025-08-16)
 
diff --git a/src/plugins/relay/api/relay-api-protocol.c b/src/plugins/relay/api/relay-api-protocol.c
index 4e318a33a..fbc8da059 100644
--- a/src/plugins/relay/api/relay-api-protocol.c
+++ b/src/plugins/relay/api/relay-api-protocol.c
@@ -1000,12 +1000,11 @@ RELAY_API_PROTOCOL_CALLBACK(completion)
         return RELAY_API_PROTOCOL_RC_MEMORY;
     }
 
-    if (!weechat_completion_search (ptr_completion, ptr_command, position, 1))
-    {
-        weechat_completion_free (ptr_completion);
-        cJSON_Delete (json_body);
-        return RELAY_API_PROTOCOL_RC_BAD_REQUEST;
-    }
+    /*
+     * ignore the return code, as 0 may indicate that completion "null" was used
+     * (that means no completion context found)
+     */
+    (void) weechat_completion_search (ptr_completion, ptr_command, position, 1);
 
     /* create response */
     json_response = relay_api_msg_completion_to_json (ptr_completion);
@@ -1035,6 +1034,11 @@ RELAY_API_PROTOCOL_CALLBACK(ping)
     json_body = cJSON_Parse (client->http_req->body);
     if (json_body)
     {
+        if (!cJSON_IsObject (json_body))
+        {
+            cJSON_Delete (json_body);
+            return RELAY_API_PROTOCOL_RC_BAD_REQUEST;
+        }
         json_data = cJSON_GetObjectItem (json_body, "data");
         if (json_data && cJSON_IsString (json_data))
             ptr_data = cJSON_GetStringValue (json_data);
diff --git a/src/plugins/relay/api/weechat-relay-api.yaml b/src/plugins/relay/api/weechat-relay-api.yaml
index cb15c671f..2c2f598dc 100644
--- a/src/plugins/relay/api/weechat-relay-api.yaml
+++ b/src/plugins/relay/api/weechat-relay-api.yaml
@@ -720,6 +720,12 @@ paths:
                 $ref: '#/components/schemas/Ping'
         '204':
           description: Successful operation
+        '400':
+          description: Bad request
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Error'
         '401':
           description: Unauthorized
           content: