diff --git a/src/pyrad3/dictionary.py b/src/pyrad3/dictionary.py
index 3578c4f..2004f9a 100644
--- a/src/pyrad3/dictionary.py
+++ b/src/pyrad3/dictionary.py
@@ -224,7 +224,7 @@ class Dictionary:
     def _parse_vendor(self, tokens: Sequence[str], line_num: int):
         """Parse the vendor definition"""
         filename = self.filestack[-1]
-        if len(tokens) not in {3, 4}:
+        if len(tokens) not in [3, 4]:
             raise ParseError(
                 filename, "Incorrect number of tokens for vendor statement"
             )
@@ -244,13 +244,13 @@ class Dictionary:
             try:
                 vendor_format = vendor_format[1].split(",")
                 t_len, l_len = (int(a) for a in vendor_format[:2])
-                if t_len not in {1, 2, 4}:
+                if t_len not in [1, 2, 4]:
                     raise ParseError(
                         filename,
                         f'Invalid type length definition "{t_len}" for vendor {vendor_name}',
                         line_num,
                     )
-                if l_len not in {0, 1, 2}:
+                if l_len not in [0, 1, 2]:
                     raise ParseError(
                         filename,
                         f'Invalid length definition "{l_len}" for vendor {vendor_name}',
@@ -399,7 +399,7 @@ class Dictionary:
     def _parse_attribute(self, tokens: Sequence[str], line_num: int):
         """Parse an ATTRIBUTE line of (Free)RADIUS dictionaries."""
         filename = self.filestack[-1]
-        if not len(tokens) in {4, 5}:
+        if not len(tokens) in [4, 5]:
             raise ParseError(
                 filename,
                 "Incorrect number of tokens for attribute definition",
@@ -410,7 +410,7 @@ class Dictionary:
         name, attr_code, datatype = tokens[1:4]
 
         if (
-            datatype in {"concat", "extended", "evs", "long-extended"}
+            datatype in ["concat", "extended", "evs", "long-extended"]
             and self.cur_vendor != self.rfc_vendor
         ):
             raise ParseError(