diff --git a/src/adapters/openai-chat.ts b/src/adapters/openai-chat.ts
index 42a923657..09c94b069 100644
--- a/src/adapters/openai-chat.ts
+++ b/src/adapters/openai-chat.ts
@@ -951,6 +951,9 @@ export function createOpenAIChatAdapter(provider: OcxProviderConfig): ProviderAd
         const rawPayload = sseFieldValue(line, "data");
         if (rawPayload === null) return "continue";
         const payload = rawPayload.trim();
+        // A bare `data:` line carries nothing (heartbeat-style keep-alive on some gateways);
+        // it is not a malformed frame, just nothing to parse.
+        if (payload.length === 0) return "continue";
         if (payload === "[DONE]") {
           yield* flushToolCalls();
           const stopReason = stopReasonFor(finishReason);
diff --git a/tests/sse-unspaced-data-fields.test.ts b/tests/sse-unspaced-data-fields.test.ts
index 3df1db33f..a1b6322c9 100644
--- a/tests/sse-unspaced-data-fields.test.ts
+++ b/tests/sse-unspaced-data-fields.test.ts
@@ -112,12 +112,23 @@ describe("openai-chat adapter (#1170)", () => {
   });
 
   test("accepts an unspaced [DONE] sentinel", async () => {
+    // Sentinel only: a preceding answer frame would let the finish-less EOF fallback emit
+    // `done` even if unspaced [DONE] handling were broken, so this test must not carry one.
+    const response = new Response("data:[DONE]\n\n");
+    const events = await collect(createOpenAIChatAdapter(provider).parseStream(response));
+    expect(events.at(-1)?.type).toBe("done");
+    expect(events.some(e => e.type === "error")).toBe(false);
+  });
+
+  test("a bare data: line is ignored, not reported as a malformed frame", async () => {
     const response = new Response([
-      'data:{"choices":[{"delta":{"content":"hi"}}]}\n\n',
-      "data:[DONE]\n\n",
+      "data:\n\n",
+      'data:{"choices":[{"delta":{"content":"hi"},"finish_reason":"stop"}]}\n\n',
     ].join(""));
     const events = await collect(createOpenAIChatAdapter(provider).parseStream(response));
+    expect(events.find(e => e.type === "text_delta")).toMatchObject({ type: "text_delta", text: "hi" });
     expect(events.at(-1)?.type).toBe("done");
+    expect(events.some(e => e.type === "error")).toBe(false);
   });
 
   test("still handles the spaced form identically", async () => {