diff --git a/lib/dbf/column.rb b/lib/dbf/column.rb
index 4017478f..b4e890ef 100644
--- a/lib/dbf/column.rb
+++ b/lib/dbf/column.rb
@@ -21,6 +21,7 @@ class NameError < StandardError
       G: ColumnType::General
     }
     TYPE_CAST_CLASS.default = ColumnType::String
+    TYPE_CAST_CLASS.freeze
 
     # Initialize a new DBF::Column
     #
diff --git a/lib/dbf/column_type.rb b/lib/dbf/column_type.rb
index 9dfae8bb..66cedbe9 100644
--- a/lib/dbf/column_type.rb
+++ b/lib/dbf/column_type.rb
@@ -4,7 +4,7 @@ class Base
       ENCODING_ARGS = [
         Encoding.default_external,
         {undef: :replace, invalid: :replace}
-      ]
+      ].freeze
 
       attr_reader :decimal, :encoding
 
diff --git a/lib/dbf/encodings.rb b/lib/dbf/encodings.rb
index 58d7aa27..040b2540 100644
--- a/lib/dbf/encodings.rb
+++ b/lib/dbf/encodings.rb
@@ -58,6 +58,6 @@ module DBF
     'c9' => 'cp1251',      # Russian Windows
     'ca' => 'cp1254',      # Turkish Windows
     'cb' => 'cp1253',      # Greek Windows
-    'cc' => 'cp1257',      # Baltic Windows
-  }
+    'cc' => 'cp1257'       # Baltic Windows
+  }.freeze
 end