diff --git a/openhands/controller/agent_controller.py b/openhands/controller/agent_controller.py
index b011a99ed4db..ad80cdcb385d 100644
--- a/openhands/controller/agent_controller.py
+++ b/openhands/controller/agent_controller.py
@@ -816,8 +816,8 @@ def _apply_conversation_window(self, events: list[Event]) -> list[Event]:
             None,
         )
 
-        # Initial cut in half
-        mid_point = len(events) // 2
+        # cut in half
+        mid_point = max(1, len(events) // 2)
         kept_events = events[mid_point:]
 
         # Handle first event in truncated history
diff --git a/tests/unit/test_truncation.py b/tests/unit/test_truncation.py
index fef0e4495193..14cb1ca0245c 100644
--- a/tests/unit/test_truncation.py
+++ b/tests/unit/test_truncation.py
@@ -86,6 +86,7 @@ def test_context_window_exceeded_handling(self, mock_event_stream, mock_agent):
         cmd1 = CmdRunAction(command='ls')
         cmd1._id = 2
         obs1 = CmdOutputObservation(command='ls', content='file1.txt', command_id=2)
+        obs1._id = 3
         obs1._cause = 2
 
         # Set up mock event stream to return our events