diff --git a/changelog.d/13789.bugfix b/changelog.d/13789.bugfix
new file mode 100644
index 000000000000..9e1e3e0fa7bf
--- /dev/null
+++ b/changelog.d/13789.bugfix
@@ -0,0 +1 @@
+Fix a long-standing spec compliance bug where Synapse would accept a trailing slash on the end of `/get_missing_events` federation requests.
\ No newline at end of file
diff --git a/synapse/federation/transport/server/federation.py b/synapse/federation/transport/server/federation.py
index f7884bfbe045..6bb4659c4c9e 100644
--- a/synapse/federation/transport/server/federation.py
+++ b/synapse/federation/transport/server/federation.py
@@ -549,8 +549,7 @@ async def on_POST(
 
 
 class FederationGetMissingEventsServlet(BaseFederationServerServlet):
-    # TODO(paul): Why does this path alone end with "/?" optional?
-    PATH = "/get_missing_events/(?P<room_id>[^/]*)/?"
+    PATH = "/get_missing_events/(?P<room_id>[^/]*)"
 
     async def on_POST(
         self,