diff --git a/src/smolagents/models.py b/src/smolagents/models.py
index 753c7c1..2dab05a 100644
--- a/src/smolagents/models.py
+++ b/src/smolagents/models.py
@@ -209,16 +209,18 @@ def get_clean_message_list(
             message["role"] = role_conversions[role]
         # encode images if needed
         if isinstance(message["content"], list):
-            for i, element in enumerate(message["content"]):
+            for element in message["content"]:
                 if element["type"] == "image":
                     assert not flatten_messages_as_text, f"Cannot use images with {flatten_messages_as_text=}"
                     if convert_images_to_image_urls:
-                        message["content"][i] = {
-                            "type": "image_url",
-                            "image_url": {"url": make_image_url(encode_image_base64(element["image"]))},
-                        }
+                        element.update(
+                            {
+                                "type": "image_url",
+                                "image_url": {"url": make_image_url(encode_image_base64(element.pop("image")))},
+                            }
+                        )
                     else:
-                        message["content"][i]["image"] = encode_image_base64(element["image"])
+                        element["image"] = encode_image_base64(element["image"])
 
         if len(output_message_list) > 0 and message["role"] == output_message_list[-1]["role"]:
             assert isinstance(message["content"], list), "Error: wrong content:" + str(message["content"])
diff --git a/tests/test_models.py b/tests/test_models.py
index aa9024c..4369844 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -17,12 +17,13 @@ import os
 import unittest
 from pathlib import Path
 from typing import Optional
+from unittest.mock import patch
 
 import pytest
 from transformers.testing_utils import get_tests_dir
 
 from smolagents import ChatMessage, HfApiModel, TransformersModel, models, tool
-from smolagents.models import parse_json_if_needed
+from smolagents.models import get_clean_message_list, parse_json_if_needed
 
 
 class ModelTests(unittest.TestCase):
@@ -100,3 +101,81 @@ class ModelTests(unittest.TestCase):
         args = 3
         parsed_args = parse_json_if_needed(args)
         assert parsed_args == 3
+
+
+def test_get_clean_message_list_basic():
+    messages = [
+        {"role": "user", "content": [{"type": "text", "text": "Hello!"}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Hi there!"}]},
+    ]
+    result = get_clean_message_list(messages)
+    assert len(result) == 2
+    assert result[0]["role"] == "user"
+    assert result[0]["content"][0]["text"] == "Hello!"
+    assert result[1]["role"] == "assistant"
+    assert result[1]["content"][0]["text"] == "Hi there!"
+
+
+def test_get_clean_message_list_role_conversions():
+    messages = [
+        {"role": "tool-call", "content": [{"type": "text", "text": "Calling tool..."}]},
+        {"role": "tool-response", "content": [{"type": "text", "text": "Tool response"}]},
+    ]
+    result = get_clean_message_list(messages, role_conversions={"tool-call": "assistant", "tool-response": "user"})
+    assert len(result) == 2
+    assert result[0]["role"] == "assistant"
+    assert result[0]["content"][0]["text"] == "Calling tool..."
+    assert result[1]["role"] == "user"
+    assert result[1]["content"][0]["text"] == "Tool response"
+
+
+@pytest.mark.parametrize(
+    "convert_images_to_image_urls, expected_clean_message",
+    [
+        (
+            False,
+            {
+                "role": "user",
+                "content": [
+                    {"type": "image", "image": "encoded_image"},
+                    {"type": "image", "image": "second_encoded_image"},
+                ],
+            },
+        ),
+        (
+            True,
+            {
+                "role": "user",
+                "content": [
+                    {"type": "image_url", "image_url": {"url": "data:image/png;base64,encoded_image"}},
+                    {"type": "image_url", "image_url": {"url": "data:image/png;base64,second_encoded_image"}},
+                ],
+            },
+        ),
+    ],
+)
+def test_get_clean_message_list_image_encoding(convert_images_to_image_urls, expected_clean_message):
+    messages = [
+        {
+            "role": "user",
+            "content": [{"type": "image", "image": b"image_data"}, {"type": "image", "image": b"second_image_data"}],
+        }
+    ]
+    with patch("smolagents.models.encode_image_base64") as mock_encode:
+        mock_encode.side_effect = ["encoded_image", "second_encoded_image"]
+        result = get_clean_message_list(messages, convert_images_to_image_urls=convert_images_to_image_urls)
+        mock_encode.assert_any_call(b"image_data")
+        mock_encode.assert_any_call(b"second_image_data")
+        assert len(result) == 1
+        assert result[0] == expected_clean_message
+
+
+def test_get_clean_message_list_flatten_messages_as_text():
+    messages = [
+        {"role": "user", "content": [{"type": "text", "text": "Hello!"}]},
+        {"role": "user", "content": [{"type": "text", "text": "How are you?"}]},
+    ]
+    result = get_clean_message_list(messages, flatten_messages_as_text=True)
+    assert len(result) == 1
+    assert result[0]["role"] == "user"
+    assert result[0]["content"] == "Hello!How are you?"