diff --git a/opendevin/observation.py b/opendevin/observation.py
index 665b7bf9bbdb..03909070810a 100644
--- a/opendevin/observation.py
+++ b/opendevin/observation.py
@@ -47,7 +47,7 @@ def error(self) -> bool:
 
     @property
     def message(self) -> str:
-        return 'The agent observed command "{self.command}" executed with exit code {self.exit_code}.'
+        return f'The agent observed command "{self.command}" executed with exit code {self.exit_code}.'
 
 
 @dataclass