diff --git a/lib/yardstick/rules/api_tag.rb b/lib/yardstick/rules/api_tag.rb
index 99e16de..6ab293e 100644
--- a/lib/yardstick/rules/api_tag.rb
+++ b/lib/yardstick/rules/api_tag.rb
@@ -24,7 +24,7 @@ def valid?
       # Checks if @api tag is a public, semipublic or private
       #
       class Inclusion < Rule
-        VALID_VALUES = %w[public semipublic private].freeze
+        VALID_VALUES = IceNine.deep_freeze(%w[public semipublic private])
 
         self.description = 'The @api tag must be either public, semipublic or private'.freeze
 
diff --git a/lib/yardstick/rules/summary.rb b/lib/yardstick/rules/summary.rb
index ae4f4e4..faa5555 100644
--- a/lib/yardstick/rules/summary.rb
+++ b/lib/yardstick/rules/summary.rb
@@ -69,7 +69,7 @@ def valid?
       # Checks that method summary length is exactly one line
       #
       class SingleLine < Rule
-        LINE_BREAK_CHARACTER = "\n"
+        LINE_BREAK_CHARACTER = "\n".freeze
 
         self.description = 'The method summary should be a single line'.freeze