diff --git a/testsuite/unittests/test_unused_names.py b/testsuite/unittests/test_unused_names.py
index f26cc8ed13..4624c12e93 100644
--- a/testsuite/unittests/test_unused_names.py
+++ b/testsuite/unittests/test_unused_names.py
@@ -83,6 +83,8 @@ def get_names(fname, pattern):
 grep_cmd = ["grep", "-ro", "names::[A-Za-Z0-9_]*", source_dir]
 names_used_raw = check_output(grep_cmd)
 
+if isinstance(names_used_raw, bytes):
+        names_used_raw = str(names_used_raw.decode())
 
 names_used = set()
 for line in names_used_raw.split("\n"):