diff --git a/spec/unit/rendezvous/MSC4108RendezvousSession.spec.ts b/spec/unit/rendezvous/MSC4108RendezvousSession.spec.ts
index a3594a31ebb..1f9360c5f74 100644
--- a/spec/unit/rendezvous/MSC4108RendezvousSession.spec.ts
+++ b/spec/unit/rendezvous/MSC4108RendezvousSession.spec.ts
@@ -210,6 +210,34 @@ describe("MSC4108RendezvousSession", () => {
         }
     });
 
+    it("GET with content-type parameters, e.g. added by an intermediary proxy", async function () {
+        const client = makeMockClient({ userId: "@alice:example.com", deviceId: "DEVICEID", msc4108Enabled: false });
+        const transport = new MSC4108RendezvousSession({
+            client,
+            fallbackRzServer: "https://fallbackserver/rz",
+        });
+        {
+            // initial POST
+            fetchMock.postOnce("https://fallbackserver/rz", {
+                status: 201,
+                body: { url: "https://fallbackserver/rz/123" },
+            });
+            await expect(transport.send("foo=baa")).resolves.toStrictEqual(undefined);
+            await fetchMock.callHistory.flush(true);
+        }
+        {
+            // GET where the content-type has a charset parameter appended, as nginx's
+            // `charset` directive does — the payload must still be received
+            fetchMock.getOnce("https://fallbackserver/rz/123", {
+                status: 200,
+                body: "foo=baa",
+                headers: { "content-type": "text/plain; charset=utf-8", "etag": "aaa" },
+            });
+            await expect(transport.receive()).resolves.toEqual("foo=baa");
+            await fetchMock.callHistory.flush(true);
+        }
+    });
+
     it("POST and PUTs", async function () {
         const client = makeMockClient({ userId: "@alice:example.com", deviceId: "DEVICEID", msc4108Enabled: false });
         const transport = new MSC4108RendezvousSession({
diff --git a/src/rendezvous/transports/MSC4108RendezvousSession.ts b/src/rendezvous/transports/MSC4108RendezvousSession.ts
index a906e014113..0af94e7442a 100644
--- a/src/rendezvous/transports/MSC4108RendezvousSession.ts
+++ b/src/rendezvous/transports/MSC4108RendezvousSession.ts
@@ -203,7 +203,10 @@ export class MSC4108RendezvousSession {
             // rely on server expiring the channel rather than checking ourselves
 
             const etag = poll.headers.get("etag") ?? undefined;
-            if (poll.headers.get("content-type") !== "text/plain") {
+            // Strip any parameters from the content type, e.g. a `charset` appended
+            // by an intermediary proxy, as only the media type itself matters.
+            const contentType = poll.headers.get("content-type")?.split(";", 1)[0].trim().toLowerCase();
+            if (contentType !== "text/plain") {
                 this.etag = etag;
             } else if (poll.status === 200) {
                 if (!etag) {