diff --git a/pelican/tests/support.py b/pelican/tests/support.py
index 3e4da785..a395eeaf 100644
--- a/pelican/tests/support.py
+++ b/pelican/tests/support.py
@@ -232,7 +232,7 @@ def diff_subproc(first, second):
          '-w', first, second],
         stdout=subprocess.PIPE,
         stderr=subprocess.PIPE,
-        text=True,
+        encoding="utf-8",
     )