diff --git a/activesupport/lib/active_support/core_ext/module/introspection.rb b/activesupport/lib/active_support/core_ext/module/introspection.rb
index bb894ec080..45f3e4bf5c 100644
--- a/activesupport/lib/active_support/core_ext/module/introspection.rb
+++ b/activesupport/lib/active_support/core_ext/module/introspection.rb
@@ -1,4 +1,14 @@
 class Module
+  # Returns the name of the module containing this one.
+  #
+  #   p M::N.parent_name # => "M"
+  def parent_name
+    unless defined? @parent_name
+      @parent_name = name =~ /::[^:]+\Z/ ? $`.freeze : nil
+    end
+    @parent_name
+  end
+
   # Returns the module which contains this one according to its name.
   #
   #   module M
@@ -16,8 +26,7 @@ class Module
   #   p Module.new.parent # => Object
   #
   def parent
-    parent_name = name.split('::')[0..-2] * '::'
-    parent_name.empty? ? Object : parent_name.constantize
+    parent_name ? parent_name.constantize : Object
   end
 
   # Returns all the parents of this module according to its name, ordered from
@@ -35,10 +44,12 @@ class Module
   #
   def parents
     parents = []
-    parts = name.split('::')[0..-2]
-    until parts.empty?
-      parents << (parts * '::').constantize
-      parts.pop
+    if parent_name
+      parts = parent_name.split('::')
+      until parts.empty?
+        parents << (parts * '::').constantize
+        parts.pop
+      end
     end
     parents << Object unless parents.include? Object
     parents