diff --git a/pymodmilter/__init__.py b/pymodmilter/__init__.py
index 902ecf1..7336703 100644
--- a/pymodmilter/__init__.py
+++ b/pymodmilter/__init__.py
@@ -111,9 +111,13 @@ setattr(email._header_value_parser, "get_name_addr", get_name_addr)
 #  add charset alias for windows-874 encoding  #
 ################################################
 
+aliases = encodings.aliases.aliases
+
 for alias in ["windows-874", "windows_874"]:
-    if alias not in encodings.aliases.aliases:
-        encodings.aliases.aliases[alias] = "cp874"
+    if alias not in aliases:
+        aliases[alias] = "cp874"
+
+setattr(encodings.aliases, "aliases", aliases)
 
 ################################################