diff --git a/python/sglang/srt/disaggregation/decode.py b/python/sglang/srt/disaggregation/decode.py
index 1ecd04ae1..25506ca33 100644
--- a/python/sglang/srt/disaggregation/decode.py
+++ b/python/sglang/srt/disaggregation/decode.py
@@ -1754,6 +1754,10 @@ class SchedulerDisaggregationDecodeMixin:
         self.result_queue = deque()
         self.last_batch: Optional[ScheduleBatch] = None
 
+        def pop_and_process():
+            tmp_batch, tmp_result = self.result_queue.popleft()
+            self.process_batch_result(tmp_batch, tmp_result)
+
         while True:
             # Receive requests
             recv_reqs = self.request_receiver.recv_requests()
@@ -1769,6 +1773,11 @@ class SchedulerDisaggregationDecodeMixin:
             # Get the next batch to run
             batch = self.get_next_disagg_decode_batch_to_run()
             self.cur_batch = batch
+            # overlap + spec + grammar is unsupported (would desync DP ranks).
+            disable_overlap_for_batch = self.is_disable_overlap_for_batch(batch)
+
+            if disable_overlap_for_batch and self.last_batch:
+                pop_and_process()
 
             # Launch the current batch
             if batch:
@@ -1779,8 +1788,8 @@ class SchedulerDisaggregationDecodeMixin:
 
             # Process the last batch
             if self.last_batch:
-                tmp_batch, tmp_result = self.result_queue.popleft()
-                self.process_batch_result(tmp_batch, tmp_result)
+                if not disable_overlap_for_batch:
+                    pop_and_process()
             elif batch is None:
                 self.on_idle()
 
diff --git a/test/registered/disaggregation/test_disaggregation_basic.py b/test/registered/disaggregation/test_disaggregation_basic.py
index 50708530f..048b3e014 100644
--- a/test/registered/disaggregation/test_disaggregation_basic.py
+++ b/test/registered/disaggregation/test_disaggregation_basic.py
@@ -10,6 +10,7 @@ import requests
 from transformers import AutoTokenizer
 
 from sglang.test.ci.ci_register import register_cuda_ci
+from sglang.test.kits.json_constrained_kit import JSONConstrainedMixin
 from sglang.test.kits.pause_generation_kit import PauseResumeInPlaceMixin
 from sglang.test.run_eval import run_eval
 from sglang.test.server_fixtures.disaggregation_fixture import (
@@ -21,7 +22,7 @@ from sglang.test.test_utils import (
     DEFAULT_TARGET_MODEL_EAGLE3,
 )
 
-register_cuda_ci(est_time=509, stage="base-b", runner_config="2-gpu-large")
+register_cuda_ci(est_time=560, stage="base-b", runner_config="2-gpu-large")
 
 
 class TestDisaggregationAccuracy(PauseResumeInPlaceMixin, PDDisaggregationServerBase):
@@ -215,7 +216,7 @@ class TestDisaggregationMooncakeFailure(PDDisaggregationServerBase):
                 raise e from health_check_error
 
 
-class TestDisaggregationMooncakeSpec(PDDisaggregationServerBase):
+class TestDisaggregationMooncakeSpec(JSONConstrainedMixin, PDDisaggregationServerBase):
     @classmethod
     def setUpClass(cls):
         super().setUpClass()