diff --git a/libs/langchain/langchain/agents/output_parsers/react_single_input.py b/libs/langchain/langchain/agents/output_parsers/react_single_input.py
index f63821588fe..b853cb04aaa 100644
--- a/libs/langchain/langchain/agents/output_parsers/react_single_input.py
+++ b/libs/langchain/langchain/agents/output_parsers/react_single_input.py
@@ -9,7 +9,7 @@ from langchain.agents.mrkl.prompt import FORMAT_INSTRUCTIONS
 
 FINAL_ANSWER_ACTION = "Final Answer:"
 MISSING_ACTION_AFTER_THOUGHT_ERROR_MESSAGE = (
-    "Invalid Format: Missing 'Action:' after 'Thought:"
+    "Invalid Format: Missing 'Action:' after 'Thought:'"
 )
 MISSING_ACTION_INPUT_AFTER_ACTION_ERROR_MESSAGE = (
     "Invalid Format: Missing 'Action Input:' after 'Action:'"