diff --git a/nbval/plugin.py b/nbval/plugin.py
index ee3ff29..c2ceec3 100644
--- a/nbval/plugin.py
+++ b/nbval/plugin.py
@@ -277,7 +277,7 @@ def setup_sanitize_files(self):
         load the contents of the file into the sanitise patterns dictionary.
         """
         for fname in self.get_sanitize_files():
-            with open(fname, 'r') as f:
+            with open(fname, 'r', encoding="utf-8") as f:
                 self.sanitize_patterns.update(get_sanitize_patterns(f.read()))