diff --git a/lib/mutant/mutation/filter.rb b/lib/mutant/mutation/filter.rb
index 16986042..ba27a573 100644
--- a/lib/mutant/mutation/filter.rb
+++ b/lib/mutant/mutation/filter.rb
@@ -54,7 +54,7 @@ module Mutant
       end
 
       # Mutation filter matching all mutations
-      Mutant.define_singleton_subclass('ALL', self) do
+      Mutant.singleton_subclass_instance('ALL', self) do
 
         # Test for match
         #
diff --git a/lib/mutant/singleton_methods.rb b/lib/mutant/singleton_methods.rb
index bc8f6a6b..373b14c7 100644
--- a/lib/mutant/singleton_methods.rb
+++ b/lib/mutant/singleton_methods.rb
@@ -10,7 +10,7 @@ module Mutant
   #
   # @api private
   #
-  def self.define_singleton_subclass(name, superclass, &block)
+  def self.singleton_subclass_instance(name, superclass, &block)
     klass = Class.new(superclass) do
 
       def inspect; self.class.name; end