diff --git a/git-filter-repo b/git-filter-repo
index 399a921..4d2562c 100755
--- a/git-filter-repo
+++ b/git-filter-repo
@@ -1655,6 +1655,7 @@ class FastExportFilter(object):
                                                    stdout=subprocess.PIPE,
                                                    cwd=self._repo_working_dir)
           batch_check_process.stdin.write(refname+"\n")
+          batch_check_process.stdin.flush()
           line = batch_check_process.stdout.readline()
           m = batch_check_output_re.match(line)
           if not m or m.group(2) != 'tag':