diff --git a/changelog.d/10175.bugfix b/changelog.d/10175.bugfix
new file mode 100644
index 0000000000..42e8f749cc
--- /dev/null
+++ b/changelog.d/10175.bugfix
@@ -0,0 +1 @@
+Fix a minor bug in the response to `/_matrix/client/r0/user/{user}/openid/request_token`. Contributed by @lukaslihotzki.
diff --git a/synapse/rest/client/v2_alpha/openid.py b/synapse/rest/client/v2_alpha/openid.py
index d3322acc38..e8d2673819 100644
--- a/synapse/rest/client/v2_alpha/openid.py
+++ b/synapse/rest/client/v2_alpha/openid.py
@@ -85,7 +85,7 @@ class IdTokenServlet(RestServlet):
                 "access_token": token,
                 "token_type": "Bearer",
                 "matrix_server_name": self.server_name,
-                "expires_in": self.EXPIRES_MS / 1000,
+                "expires_in": self.EXPIRES_MS // 1000,
             },
         )