diff --git a/mitmproxy/tools/web/app.py b/mitmproxy/tools/web/app.py
index 6bdd7eb1c..f6f975928 100644
--- a/mitmproxy/tools/web/app.py
+++ b/mitmproxy/tools/web/app.py
@@ -93,6 +93,8 @@ def flow_to_json(flow: mitmproxy.flow.Flow) -> dict:
                 "timestamp_end": flow.response.timestamp_end,
                 "is_replay": flow.response.is_replay,
             }
+        if flow.trailers:
+            f["trailers"] = tuple(flow.trailers.items(True))
     f.get("server_conn", {}).pop("cert", None)
     f.get("client_conn", {}).pop("mitmcert", None)