diff --git a/monitoring/monitorlib/fetch/__init__.py b/monitoring/monitorlib/fetch/__init__.py
index a9ced61b54..5a71144fe5 100644
--- a/monitoring/monitorlib/fetch/__init__.py
+++ b/monitoring/monitorlib/fetch/__init__.py
@@ -315,7 +315,7 @@ def query_and_describe(
         req_kwargs["timeout"] = TIMEOUTS
 
     # Attach a request_id field to the JSON body of any outgoing request with a JSON body that doesn't already have one
-    if "json" in req_kwargs and "request_id" not in req_kwargs["json"]:
+    if "json" in req_kwargs and isinstance(req_kwargs["json"], dict) and "request_id" not in req_kwargs["json"]:
         json_body = json.loads(json.dumps(req_kwargs["json"]))
         json_body["request_id"] = str(uuid.uuid4())
         req_kwargs["json"] = json_body