diff --git a/changelog.d/15001.misc b/changelog.d/15001.misc
new file mode 100644
index 0000000000..c20faf2358
--- /dev/null
+++ b/changelog.d/15001.misc
@@ -0,0 +1 @@
+Increase client timeout for potentially long federation requests. It should improve joining behavior of big rooms.
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 5e36638b0a..05bd75de26 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -83,6 +83,8 @@ class TransportLayerClient:
             destination,
             path=path,
             args={"event_id": event_id},
+            # This can take a looooooong time for large rooms.
+            timeout=600_000,
             try_trailing_slash_on_400=True,
         )
 
@@ -351,6 +353,8 @@ class TransportLayerClient:
             destination=destination,
             path=path,
             data=content,
+            # This can take a looooooong time for large rooms.
+            timeout=600_000,
             parser=SendJoinParser(room_version, v1_api=True),
         )
 
@@ -373,6 +377,8 @@ class TransportLayerClient:
             path=path,
             args=query_params,
             data=content,
+            # This can take a looooooong time for large rooms.
+            timeout=600_000,
             parser=SendJoinParser(room_version, v1_api=False),
         )