diff --git a/python/extensions/system_prompt/_20_behaviour_prompt.py b/python/extensions/system_prompt/_20_behaviour_prompt.py
index bdcadc261..5c451eba7 100644
--- a/python/extensions/system_prompt/_20_behaviour_prompt.py
+++ b/python/extensions/system_prompt/_20_behaviour_prompt.py
@@ -16,7 +16,7 @@ def get_custom_rules_file(agent: Agent):
 def read_rules(agent: Agent):
     rules_file = get_custom_rules_file(agent)
     if files.exists(rules_file):
-        rules = files.read_prompt_file(rules_file)
+        rules = files.read_file(rules_file) # no includes and vars here, that could crash
         return agent.read_prompt("agent.system.behaviour.md", rules=rules)
     else:
         rules = agent.read_prompt("agent.system.behaviour_default.md")