diff --git a/src/smolagents/agents.py b/src/smolagents/agents.py
index 5e5fe41..73b2647 100644
--- a/src/smolagents/agents.py
+++ b/src/smolagents/agents.py
@@ -529,9 +529,9 @@ You have been provided with these additional arguments, that you can access usin
                 level=LogLevel.INFO,
             )
         else:  # update plan
-            memory_messages = self.write_memory_to_messages(
-                summary_mode=False
-            )  # This will not log the plan but will log facts
+            # Do not take the system prompt message from the memory
+            # summary_mode=False: Do not take previous plan steps to avoid influencing the new plan
+            memory_messages = self.write_memory_to_messages()[1:]
 
             # Redact updated facts
             facts_update_pre_messages = {
diff --git a/tests/test_agents.py b/tests/test_agents.py
index 631ccf8..b097132 100644
--- a/tests/test_agents.py
+++ b/tests/test_agents.py
@@ -690,27 +690,61 @@ class TestMultiStepAgent:
         assert hasattr(agent, "step_number"), "step_number attribute should be defined"
         assert agent.step_number == max_steps + 1, "step_number should be max_steps + 1 after run method is called"
 
-    def test_planning_step_first_step(self):
+    @pytest.mark.parametrize(
+        "step, expected_messages_list",
+        [
+            (
+                1,
+                [
+                    [
+                        {"role": MessageRole.SYSTEM, "content": [{"type": "text", "text": "FACTS_SYSTEM_PROMPT"}]},
+                        {"role": MessageRole.USER, "content": [{"type": "text", "text": "FACTS_USER_PROMPT"}]},
+                    ],
+                    [{"role": MessageRole.USER, "content": [{"type": "text", "text": "PLAN_USER_PROMPT"}]}],
+                ],
+            ),
+            (
+                2,
+                [
+                    [
+                        {
+                            "role": MessageRole.SYSTEM,
+                            "content": [{"type": "text", "text": "FACTS_UPDATE_SYSTEM_PROMPT"}],
+                        },
+                        {"role": MessageRole.USER, "content": [{"type": "text", "text": "FACTS_UPDATE_USER_PROMPT"}]},
+                    ],
+                    [
+                        {
+                            "role": MessageRole.SYSTEM,
+                            "content": [{"type": "text", "text": "PLAN_UPDATE_SYSTEM_PROMPT"}],
+                        },
+                        {"role": MessageRole.USER, "content": [{"type": "text", "text": "PLAN_UPDATE_USER_PROMPT"}]},
+                    ],
+                ],
+            ),
+        ],
+    )
+    def test_planning_step_first_step(self, step, expected_messages_list):
         fake_model = MagicMock()
         agent = CodeAgent(
             tools=[],
             model=fake_model,
         )
         task = "Test task"
-        agent.planning_step(task, is_first_step=True, step=0)
+        agent.planning_step(task, is_first_step=(step == 1), step=step)
         assert len(agent.memory.steps) == 1
         planning_step = agent.memory.steps[0]
         assert isinstance(planning_step, PlanningStep)
-        messages = planning_step.model_input_messages
-        assert isinstance(messages, list)
-        assert len(messages) == 2
-        expected_roles = [MessageRole.SYSTEM, MessageRole.USER]
-        for i, message in enumerate(messages):
+        expected_model_input_messages = expected_messages_list[0]
+        model_input_messages = planning_step.model_input_messages
+        assert isinstance(model_input_messages, list)
+        assert len(model_input_messages) == len(expected_model_input_messages)  # 2
+        for message, expected_message in zip(model_input_messages, expected_model_input_messages):
             assert isinstance(message, dict)
             assert "role" in message
             assert "content" in message
             assert isinstance(message["role"], MessageRole)
-            assert message["role"] == expected_roles[i]
+            assert message["role"] == expected_message["role"]
             assert isinstance(message["content"], list)
             assert len(message["content"]) == 1
             for content in message["content"]:
@@ -719,16 +753,17 @@ class TestMultiStepAgent:
                 assert "text" in content
         # Test calls to model
         assert len(fake_model.call_args_list) == 2
-        for call_args in fake_model.call_args_list:
+        for call_args, expected_messages in zip(fake_model.call_args_list, expected_messages_list):
             assert len(call_args.args) == 1
             messages = call_args.args[0]
             assert isinstance(messages, list)
-            # assert len(messages) == 1  # TODO
-            for message in messages:
+            assert len(messages) == len(expected_messages)
+            for message, expected_message in zip(messages, expected_messages):
                 assert isinstance(message, dict)
                 assert "role" in message
                 assert "content" in message
                 assert isinstance(message["role"], MessageRole)
+                assert message["role"] == expected_message["role"]
                 assert isinstance(message["content"], list)
                 assert len(message["content"]) == 1
                 for content in message["content"]: