diff --git a/openhands/memory/condenser/condenser.py b/openhands/memory/condenser/condenser.py
index 723473c6aab9..411ed39386f6 100644
--- a/openhands/memory/condenser/condenser.py
+++ b/openhands/memory/condenser/condenser.py
@@ -161,13 +161,13 @@ def __init__(self) -> None:
 
     @override
     def condensed_history(self, state: State) -> list[Event]:
-        # If history has been truncated, reset the condenser state
+        # The history should grow monotonically -- if it doesn't, something has
+        # truncated the history and we need to reset our tracking.
         if len(state.history) < self._last_history_length:
             self._condensation = []
             self._last_history_length = 0
-            new_events = state.history
-        else:
-            new_events = state.history[self._last_history_length :]
+
+        new_events = state.history[self._last_history_length :]
 
         with self.metadata_batch(state):
             results = self.condense(self._condensation + new_events)
diff --git a/tests/unit/test_condenser.py b/tests/unit/test_condenser.py
index 0179fb9ba142..fd1e922a103a 100644
--- a/tests/unit/test_condenser.py
+++ b/tests/unit/test_condenser.py
@@ -453,18 +453,16 @@ def test_llm_attention_condenser_invalid_config():
     pytest.raises(ValueError, LLMAttentionCondenser.from_config, config)
 
 
-class TestRollingCondenser(RollingCondenser):
-    """Test implementation of RollingCondenser that just returns all events."""
+def test_rolling_condenser_handles_truncation(mock_state: State):
+    """Test that RollingCondenser correctly handles history truncation."""
 
-    def condense(self, events: list[Event]) -> list[Event]:
-        return events
+    class TestRollingCondenser(RollingCondenser):
+        """Test implementation of RollingCondenser that just returns all events."""
 
+        def condense(self, events: list[Event]) -> list[Event]:
+            return events
 
-def test_rolling_condenser_handles_truncation():
-    """Test that RollingCondenser correctly handles history truncation."""
     condenser = TestRollingCondenser()
-    mock_state = MagicMock(spec=State)
-    mock_state.extra_data = {}
 
     # Initial history with 3 events
     events = [
@@ -479,29 +477,23 @@ def test_rolling_condenser_handles_truncation():
     assert len(results) == 3
     assert [e._id for e in results] == [1, 2, 3]
 
-    # Add 2 more events
-    events.extend([
-        create_test_event('Event 4', id=4),
-        create_test_event('Event 5', id=5),
-    ])
-    mock_state.history = events
+    # Simulate truncation - history is now shorter, and the condensation should
+    # just include the truncated history
+    mock_state.history = mock_state.history[-1:]
 
-    # Second condensation - should return all 5 events
     results = condenser.condensed_history(mock_state)
-    assert len(results) == 5
-    assert [e._id for e in results] == [1, 2, 3, 4, 5]
+    assert len(results) == 1
+    assert results[0]._id == 3
 
-    # Simulate truncation - history is now shorter
-    truncated_events = [
+    # Adding more events and condensing should "rebase" us from the truncated history
+    mock_state.history += [
         create_test_event('Event 4', id=4),
         create_test_event('Event 5', id=5),
     ]
-    mock_state.history = truncated_events
 
-    # Third condensation - should handle truncation gracefully
     results = condenser.condensed_history(mock_state)
-    assert len(results) == 2
-    assert [e._id for e in results] == [4, 5]
+    assert len(results) == 3
+    assert [e._id for e in results] == [3, 4, 5]
 
 
 def test_llm_attention_condenser_keeps_first_events(mock_llm, mock_state):