diff --git a/taf/git.py b/taf/git.py
index 78e809da..0d750b40 100644
--- a/taf/git.py
+++ b/taf/git.py
@@ -400,7 +400,7 @@ def all_commits_since_commit(
             try:
                 return self.all_commits_on_branch(branch=branch, reverse=reverse)
             except GitError as e:
-                self._log_warning(e)
+                self._log_warning(str(e))
                 return []
 
         try: