diff --git a/src/memos/mem_scheduler/memory_manage_modules/memory_filter.py b/src/memos/mem_scheduler/memory_manage_modules/memory_filter.py
index 25b9a98f3..a11ee88ea 100644
--- a/src/memos/mem_scheduler/memory_manage_modules/memory_filter.py
+++ b/src/memos/mem_scheduler/memory_manage_modules/memory_filter.py
@@ -234,10 +234,6 @@ def filter_unrelated_and_redundant_memories(
             logger.info("No query history provided - keeping all memories")
             return memories, True
 
-        if len(memories) <= 1:
-            logger.info("Only one memory - no filtering needed")
-            return memories, True
-
         logger.info(
             f"Starting combined unrelated and redundant filtering for {len(memories)} memories against {len(query_history)} queries"
         )
diff --git a/tests/mem_scheduler/test_retriever.py b/tests/mem_scheduler/test_retriever.py
index 35c8b7f3a..a40203316 100644
--- a/tests/mem_scheduler/test_retriever.py
+++ b/tests/mem_scheduler/test_retriever.py
@@ -360,3 +360,54 @@ def test_filter_unrelated_memories_conservative_filtering(self):
         # Should return all memories
         self.assertEqual(result, memories)
         self.assertTrue(success_flag)
+        self.assertTrue(self.llm.generate.called)
+
+    def test_combined_filtering_still_filters_a_single_unrelated_memory(self):
+        """A lone memory must still go through unrelated filtering.
+
+        The combined filter used to return early on `len(memories) <= 1`, a
+        guard that only makes sense for redundancy (one memory cannot be
+        redundant with itself). Unrelated filtering is per-memory, so skipping
+        it left an off-topic memory sitting in working memory.
+        """
+        query_history = ["What is my deployment pipeline?"]
+        memories = [TextualMemoryItem(memory="The user's cat is named Whiskers")]
+
+        self.llm.generate.return_value = json.dumps(
+            {
+                "kept_memories": [],
+                "unrelated_removed_count": 1,
+                "redundant_removed_count": 0,
+                "reasoning": "No semantic connection to the deployment query",
+            }
+        )
+
+        result, success_flag = self.retriever.filter_unrelated_and_redundant_memories(
+            query_history=query_history, memories=memories
+        )
+
+        self.assertEqual(result, [])
+        self.assertTrue(success_flag)
+        # The LLM must actually be consulted, not short-circuited.
+        self.assertTrue(self.llm.generate.called)
+
+    def test_combined_filtering_keeps_a_single_relevant_memory(self):
+        """The counterpart: one on-topic memory must survive the filter."""
+        query_history = ["What is my deployment pipeline?"]
+        memories = [TextualMemoryItem(memory="Deployment uses a blue-green pipeline")]
+
+        self.llm.generate.return_value = json.dumps(
+            {
+                "kept_memories": [0],
+                "unrelated_removed_count": 0,
+                "redundant_removed_count": 0,
+                "reasoning": "Directly answers the deployment query",
+            }
+        )
+
+        result, success_flag = self.retriever.filter_unrelated_and_redundant_memories(
+            query_history=query_history, memories=memories
+        )
+
+        self.assertEqual(result, memories)
+        self.assertTrue(success_flag)