diff --git a/libs/core/langchain_core/messages/base.py b/libs/core/langchain_core/messages/base.py
index 60c57220033..d73b4d526b3 100644
--- a/libs/core/langchain_core/messages/base.py
+++ b/libs/core/langchain_core/messages/base.py
@@ -1,11 +1,11 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Any, Dict, List, Optional, Sequence, Union
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Sequence, Union, cast
 
 from langchain_core.load.serializable import Serializable
 from langchain_core.pydantic_v1 import Extra, Field
 from langchain_core.utils import get_bolded_text
-from langchain_core.utils._merge import merge_dicts
+from langchain_core.utils._merge import merge_dicts, merge_lists
 from langchain_core.utils.interactive_env import is_interactive_env
 
 if TYPE_CHECKING:
@@ -95,9 +95,10 @@ def merge_content(
         else:
             return_list: List[Union[str, Dict]] = [first_content]
             return return_list + second_content
-    # If both are lists, merge them naively
     elif isinstance(second_content, List):
-        return first_content + second_content
+        # If both are lists
+        merged_list = merge_lists(first_content, second_content)
+        return cast(list, merged_list)
     # If the first content is a list, and the second content is a string
     else:
         # If the last element of the first content is a string
diff --git a/libs/core/tests/unit_tests/test_messages.py b/libs/core/tests/unit_tests/test_messages.py
index 21884cf1e83..c893f8ced57 100644
--- a/libs/core/tests/unit_tests/test_messages.py
+++ b/libs/core/tests/unit_tests/test_messages.py
@@ -162,6 +162,48 @@ def test_chat_message_chunks() -> None:
     ), "Other MessageChunk + ChatMessageChunk should be a MessageChunk as the left side"
 
 
+def test_complex_ai_message_chunks() -> None:
+    assert AIMessageChunk(content=["I am"], id="ai4") + AIMessageChunk(
+        content=[" indeed."]
+    ) == AIMessageChunk(
+        id="ai4", content=["I am", " indeed."]
+    ), "Content concatenation with arrays of strings should naively combine"
+
+    assert AIMessageChunk(content=[{"index": 0, "text": "I am"}]) + AIMessageChunk(
+        content=" indeed."
+    ) == AIMessageChunk(
+        content=[{"index": 0, "text": "I am"}, " indeed."]
+    ), "Concatenating mixed content arrays should naively combine them"
+
+    assert (
+        AIMessageChunk(content=[{"index": 0, "text": "I am"}])
+        + AIMessageChunk(content=[{"index": 0, "text": " indeed."}])
+        == AIMessageChunk(content=[{"index": 0, "text": "I am indeed."}])
+    ), "Concatenating when both content arrays are dicts with the same index should merge"  # noqa: E501
+
+    assert AIMessageChunk(content=[{"index": 0, "text": "I am"}]) + AIMessageChunk(
+        content=[{"text": " indeed."}]
+    ) == AIMessageChunk(
+        content=[{"index": 0, "text": "I am"}, {"text": " indeed."}]
+    ), "Concatenating when one chunk is missing an index should not merge or throw"  # noqa: E501
+
+    assert (
+        AIMessageChunk(content=[{"index": 0, "text": "I am"}])
+        + AIMessageChunk(content=[{"index": 2, "text": " indeed."}])
+        == AIMessageChunk(
+            content=[{"index": 0, "text": "I am"}, {"index": 2, "text": " indeed."}]
+        )
+    ), "Concatenating when both content arrays are dicts with a gap between indexes should not result in a holey array"  # noqa: E501
+
+    assert (
+        AIMessageChunk(content=[{"index": 0, "text": "I am"}])
+        + AIMessageChunk(content=[{"index": 1, "text": " indeed."}])
+        == AIMessageChunk(
+            content=[{"index": 0, "text": "I am"}, {"index": 1, "text": " indeed."}]
+        )
+    ), "Concatenating when both content arrays are dicts with separate indexes should not merge"  # noqa: E501
+
+
 def test_function_message_chunks() -> None:
     assert FunctionMessageChunk(
         name="hello", content="I am", id="ai5"