diff --git a/scmrepo/fs.py b/scmrepo/fs.py
index b0908cd8..09d0ceb7 100644
--- a/scmrepo/fs.py
+++ b/scmrepo/fs.py
@@ -90,7 +90,7 @@ def _open(
             obj.size = bytesio_len(obj)
             return obj
         except KeyError as exc:
-            msg = os.strerror(errno.ENOENT) + f"in branch '{self.rev}'"
+            msg = os.strerror(errno.ENOENT) + f" in branch '{self.rev}'"
             raise FileNotFoundError(errno.ENOENT, msg, path) from exc
         except IsADirectoryError as exc:
             raise IsADirectoryError(
diff --git a/scmrepo/git/backend/pygit2.py b/scmrepo/git/backend/pygit2.py
index 58e6e3b0..d483efc8 100644
--- a/scmrepo/git/backend/pygit2.py
+++ b/scmrepo/git/backend/pygit2.py
@@ -646,7 +646,7 @@ def merge(
                         return str(obj.id)
 
                 if ff_pref & GIT_MERGE_PREFERENCE_FASTFORWARD_ONLY:
-                    raise SCMError("Cannot fast-forward HEAD to '{rev}'")
+                    raise SCMError(f"Cannot fast-forward HEAD to '{rev}'")
 
                 if commit:
                     if not msg: