diff --git a/mem0/memory/main.py b/mem0/memory/main.py
index e7252f95e..ec9dd202e 100644
--- a/mem0/memory/main.py
+++ b/mem0/memory/main.py
@@ -656,10 +656,10 @@ class Memory(MemoryBase):
         else:
             messages = parse_vision_messages(messages)
 
-        vector_store_result = self._add_to_vector_store(messages, processed_metadata, effective_filters, infer)
+        vector_store_result = self._add_to_vector_store(messages, processed_metadata, effective_filters, infer, prompt=prompt)
         return {"results": vector_store_result}
 
-    def _add_to_vector_store(self, messages, metadata, filters, infer):
+    def _add_to_vector_store(self, messages, metadata, filters, infer, prompt=None):
         if not infer:
             returned_memories = []
             for message_dict in messages:
@@ -726,7 +726,7 @@ class Memory(MemoryBase):
         if is_agent_scoped:
             system_prompt += AGENT_CONTEXT_SUFFIX
 
-        custom_instr = self.custom_instructions
+        custom_instr = prompt or self.custom_instructions
 
         user_prompt = generate_additive_extraction_prompt(
             existing_memories=existing_memories,
@@ -2064,7 +2064,7 @@ class AsyncMemory(MemoryBase):
         else:
             messages = parse_vision_messages(messages)
 
-        vector_store_result = await self._add_to_vector_store(messages, processed_metadata, effective_filters, infer)
+        vector_store_result = await self._add_to_vector_store(messages, processed_metadata, effective_filters, infer, prompt=prompt)
         return {"results": vector_store_result}
 
     async def _add_to_vector_store(
@@ -2073,6 +2073,7 @@ class AsyncMemory(MemoryBase):
         metadata: dict,
         effective_filters: dict,
         infer: bool,
+        prompt: Optional[str] = None,
     ):
         if not infer:
             returned_memories = []
@@ -2141,7 +2142,7 @@ class AsyncMemory(MemoryBase):
         if is_agent_scoped:
             system_prompt += AGENT_CONTEXT_SUFFIX
 
-        custom_instr = self.custom_instructions
+        custom_instr = prompt or self.custom_instructions
 
         user_prompt = generate_additive_extraction_prompt(
             existing_memories=existing_memories,
diff --git a/tests/memory/test_main.py b/tests/memory/test_main.py
index 94e4883e0..3631162a3 100644
--- a/tests/memory/test_main.py
+++ b/tests/memory/test_main.py
@@ -78,6 +78,43 @@ class TestAddToVectorStoreErrors:
         assert result == []  # Should return empty list when no memories processed
 
 
+class TestPromptOverridesCustomInstructions:
+    @pytest.fixture
+    def mock_memory(self, mocker):
+        mock_llm, _ = _setup_mocks(mocker)
+        mock_llm.return_value.generate_response.return_value = '{"memory": []}'
+
+        memory = Memory()
+        memory.custom_instructions = "config-level instructions"
+        memory.db.get_last_messages = MagicMock(return_value=[])
+        memory.db.save_messages = MagicMock()
+        return memory
+
+    def test_prompt_overrides_custom_instructions(self, mock_memory):
+        mock_memory._add_to_vector_store(
+            messages=[{"role": "user", "content": "hello"}],
+            metadata={},
+            filters={},
+            infer=True,
+            prompt="per-call override",
+        )
+
+        user_prompt = mock_memory.llm.generate_response.call_args[1]["messages"][1]["content"]
+        assert "per-call override" in user_prompt
+        assert "config-level instructions" not in user_prompt
+
+    def test_falls_back_to_custom_instructions_when_no_prompt(self, mock_memory):
+        mock_memory._add_to_vector_store(
+            messages=[{"role": "user", "content": "hello"}],
+            metadata={},
+            filters={},
+            infer=True,
+        )
+
+        user_prompt = mock_memory.llm.generate_response.call_args[1]["messages"][1]["content"]
+        assert "config-level instructions" in user_prompt
+
+
 class TestAsyncUpdate:
     @pytest.fixture
     def mock_async_memory(self, mocker):
diff --git a/tests/test_main.py b/tests/test_main.py
index fc2829c6b..ae105b9de 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -61,7 +61,7 @@ def test_add(memory_instance):
     assert result["results"] == [{"memory": "Test memory", "event": "ADD"}]
 
     memory_instance._add_to_vector_store.assert_called_once_with(
-        [{"role": "user", "content": "Test message"}], {"user_id": "test_user"}, {"user_id": "test_user"}, True
+        [{"role": "user", "content": "Test message"}], {"user_id": "test_user"}, {"user_id": "test_user"}, True, prompt=None
     )