diff --git a/git-filter-repo b/git-filter-repo
index 60ff51f..a76b90f 100755
--- a/git-filter-repo
+++ b/git-filter-repo
@@ -432,12 +432,12 @@ class _GitElement(object):
     raise SystemExit(_("Unimplemented function: %s") % type(self).__name__
                      +".dump()") # pragma: no cover
 
-  def __str__(self):
+  def __bytes__(self):
     """
     Convert GitElement to string; used for debugging
     """
     old_dumped = self.dumped
-    writeme = io.StringIO()
+    writeme = io.BytesIO()
     self.dump(writeme)
     output_lines = writeme.getvalue().splitlines()
     writeme.close()
diff --git a/t/t9391/unusual.py b/t/t9391/unusual.py
index 6817c65..c7a2c57 100755
--- a/t/t9391/unusual.py
+++ b/t/t9391/unusual.py
@@ -50,7 +50,7 @@ compare = "Blob:\n  blob\n  mark :1\n  data {}\n  {}".format(len(mystr), mystr)
 # debugging git-filter-repo; it is NOT something external folks should depend
 # upon.
 myblob = fr.Blob(mystr)
-assert str(myblob) == compare
+assert bytes(myblob) == compare
 # Everyone should be using RepoFilter objects, not FastExportFilter.  But for
 # testing purposes...
 filter = fr.FastExportFilter('.',
@@ -71,7 +71,7 @@ print("Found {} blobs/commits and {} other objects"
       .format(total_objects['common'], total_objects['uncommon']))
 
 
-stream = io.StringIO(textwrap.dedent('''
+stream = io.BytesIO(textwrap.dedent('''
   blob
   mark :1
   data 5