diff --git a/libs/core/langchain_core/messages/utils.py b/libs/core/langchain_core/messages/utils.py
index 520ae13322..edda11d155 100644
--- a/libs/core/langchain_core/messages/utils.py
+++ b/libs/core/langchain_core/messages/utils.py
@@ -440,7 +440,7 @@ def merge_message_runs(
 
             [
                 SystemMessage("you're a good assistant."),
-                HumanMessage("what's your favorite color\nwait your favorite food", id="foo",),
+                HumanMessage("what's your favorite color\\nwait your favorite food", id="foo",),
                 AIMessage(
                     [
                         "my favorite colo",