diff --git a/python/packages/ag-ui/agent_framework_ag_ui/_http_service.py b/python/packages/ag-ui/agent_framework_ag_ui/_http_service.py
index f13d749080e..e4751dfd884 100644
--- a/python/packages/ag-ui/agent_framework_ag_ui/_http_service.py
+++ b/python/packages/ag-ui/agent_framework_ag_ui/_http_service.py
@@ -269,8 +269,11 @@ async def exit_response(
 
             async for line in response.aiter_lines():
                 # Parse Server-Sent Events format
-                if line.startswith("data: "):
-                    data = line[6:]  # Remove "data: " prefix
+                if line.startswith("data:"):
+                    data = line[5:]
+                    # The space after "data:" is optional in SSE.
+                    if data.startswith(" "):
+                        data = data[1:]
                     try:
                         event = json.loads(data)
                         logger.debug(f"Received event: {event.get('type', 'UNKNOWN')}")
diff --git a/python/packages/ag-ui/tests/ag_ui/test_http_service.py b/python/packages/ag-ui/tests/ag_ui/test_http_service.py
index a758c2abaa5..fbf4f9a8bfd 100644
--- a/python/packages/ag-ui/tests/ag_ui/test_http_service.py
+++ b/python/packages/ag-ui/tests/ag_ui/test_http_service.py
@@ -317,6 +317,20 @@ async def mock_aiter_lines():
     assert events[0]["type"] == "RUN_FINISHED"
 
 
+async def test_post_run_accepts_data_lines_without_space(sample_events):
+    """The space after "data:" is optional in SSE, so "data:{...}" lines must be parsed too."""
+    body = "".join(f"data:{json.dumps(event)}\n\n" for event in sample_events)
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        return httpx.Response(200, headers={"content-type": "text/event-stream"}, text=body)
+
+    async with httpx.AsyncClient(transport=httpx.MockTransport(handler)) as client:
+        service = AGUIHttpService("http://localhost:8888/", http_client=client)
+        events = [event async for event in service.post_run(thread_id="thread_123", run_id="run_456", messages=[])]
+
+    assert events == sample_events
+
+
 async def test_context_manager():
     """Test context manager functionality."""
     async with AGUIHttpService("http://localhost:8888/") as service: