pythonthings
diff --git a/‎python/phonenumbers/phonenumberutil.py‎
Lines changed: 1 addition & 1 deletion b/‎python/phonenumbers/phonenumberutil.py‎
Lines changed: 1 addition & 1 deletion
@@ -95,7 +95,7 @@
 # in China mobile numbers start with a carrier indicator, and beyond that are
 # geographically assigned: this carrier indicator is not considered to be an
 # area code.
-_GEO_MOBILE_COUNTRIES_WITHOUT_MOBILE_AREA_CODES = set((
+_GEO_MOBILE_COUNTRIES_WITHOUT_MOBILE_AREA_CODES = frozenset((
     86,))  # China
 # Set of country calling codes that have geographically assigned mobile
 # numbers. This may not be complete; we add calling codes case by case, as we