diff --git a/src/adapters/openai-chat.ts b/src/adapters/openai-chat.ts
index 7e8aff56c..09b4d74e9 100644
--- a/src/adapters/openai-chat.ts
+++ b/src/adapters/openai-chat.ts
@@ -947,8 +947,14 @@ export function createOpenAIChatAdapter(provider: OcxProviderConfig): ProviderAd
       // Yields adapter events and returns "terminate" for a terminal frame ([DONE] / error) that
       // must end the stream, or "continue" otherwise. Mutates the closure's terminal-signal state.
       const handleDataLine = function* (line: string): Generator<AdapterEvent, "continue" | "terminate"> {
-        if (!line.startsWith("data: ")) return "continue";
-        const payload = line.slice(6).trim();
+        // SSE field syntax: the value may begin immediately after the colon; one optional
+        // leading space is stripped when present. Some OpenAI-compatible upstreams emit
+        // `data:{...}` / `data:[DONE]` without that space, and every frame was dropped.
+        if (!line.startsWith("data:")) return "continue";
+        const payload = line.slice(5).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/openai-chat-eof.test.ts b/tests/openai-chat-eof.test.ts
index 4031b1e0a..90b06aede 100644
--- a/tests/openai-chat-eof.test.ts
+++ b/tests/openai-chat-eof.test.ts
@@ -293,3 +293,51 @@ describe("openai-chat EOF mid tool call (#735)", () => {
     expect(events.at(-1)?.type).toBe("done");
   });
 });
+
+describe("openai-chat SSE data-field framing (#1170)", () => {
+  // The SSE spec strips at most one optional space after the colon, so `data:{...}` is a valid
+  // data field. Some OpenAI-compatible gateways emit that framing; the parser must accept it
+  // exactly like the spaced form.
+  test("unspaced data:{...} frames with a final finish_reason and no [DONE] complete", async () => {
+    const response = new Response([
+      'data:{"id":"x","object":"chat.completion.chunk","choices":[{"index":0,"delta":{"content":"hi"},"finish_reason":null}]}\n\n',
+      'data:{"id":"x","object":"chat.completion.chunk","choices":[{"index":0,"delta":{},"finish_reason":"length"}]}\n\n',
+      'data:{"id":"x","object":"chat.completion.chunk","choices":[],"usage":{"prompt_tokens":1,"completion_tokens":2,"total_tokens":3}}\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" });
+    // "length" maps to stopReason "max_tokens" ("stop" maps to none): the EOF fallback would
+    // emit done WITHOUT a stopReason, so this assertion only passes if the terminal
+    // finish_reason frame was actually parsed.
+    expect(events.at(-1)).toMatchObject({ type: "done", stopReason: "max_tokens" });
+    expect(events.some(e => e.type === "error")).toBe(false);
+  });
+
+  test("unspaced data:[DONE] sentinel terminates the stream", async () => {
+    // Sentinel only: a preceding answer frame would let the finish_reason 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:\n\n",
+      'data:{"choices":[{"delta":{"content":"hi"},"finish_reason":"stop"}]}\n\n',
+    ].join(""));
+    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("unspaced truncated stream with no terminal signal still fails closed", async () => {
+    const response = new Response(
+      'data:{"choices":[{"delta":{"reasoning_content":"thinking..."}}]}\n\n',
+    );
+    const events = await collect(createOpenAIChatAdapter(provider).parseStream(response));
+    expect(events.at(-1)?.type).toBe("error");
+    expect(events.some(e => e.type === "done")).toBe(false);
+  });
+});