diff --git a/langchain/agents/mrkl/prompt.py b/langchain/agents/mrkl/prompt.py
index c32310d4..2f0e207c 100644
--- a/langchain/agents/mrkl/prompt.py
+++ b/langchain/agents/mrkl/prompt.py
@@ -10,6 +10,8 @@ Observation: the result of the action
 ... (this Thought/Action/Action Input/Observation can repeat N times)
 Thought: I now know the final answer
 Final Answer: the final answer to the original input question"""
-SUFFIX = """Begin!
+SUFFIX = """Do NOT use any tools that do not exist.
+
+Begin!
 
 Question: {input}"""