diff --git a/Lib/site.py b/Lib/site.py
index 6f66c07de5f..3a8d1c37283 100644
--- a/Lib/site.py
+++ b/Lib/site.py
@@ -465,7 +465,9 @@ def venv(known_paths):
         config_line = re.compile(CONFIG_LINE)
         virtual_conf = candidate_confs[0]
         system_site = "true"
-        with open(virtual_conf) as f:
+        # Issue 25185: Use UTF-8, as that's what the venv module uses when
+        # writing the file.
+        with open(virtual_conf, encoding='utf-8') as f:
             for line in f:
                 line = line.strip()
                 m = config_line.match(line)