diff --git a/tests/test_rustbpe.py b/tests/test_rustbpe.py
index 5f95721..aca67fc 100644
--- a/tests/test_rustbpe.py
+++ b/tests/test_rustbpe.py
@@ -455,13 +455,13 @@ def enwik8_path():
 @pytest.fixture(scope="module")
 def enwik8_small(enwik8_path):
     """Fixture providing 100KB of enwik8 for quick tests."""
-    with open(enwik8_path, "r") as f:
+    with open(enwik8_path, "r", encoding="utf-8") as f:
         return f.read(100_000)
 
 @pytest.fixture(scope="module")
 def enwik8_large(enwik8_path):
     """Fixture providing 10MB of enwik8 for performance tests."""
-    with open(enwik8_path, "r") as f:
+    with open(enwik8_path, "r", encoding="utf-8") as f:
         return f.read(10**7)
 
 def time_function(func, *args, **kwargs):