diff --git a/activemodel/lib/active_model/observing.rb b/activemodel/lib/active_model/observing.rb
index 14f8bf72dc472..d0f36ce3b1046 100644
--- a/activemodel/lib/active_model/observing.rb
+++ b/activemodel/lib/active_model/observing.rb
@@ -2,7 +2,6 @@
 require 'active_support/core_ext/array/wrap'
 require 'active_support/core_ext/module/aliasing'
 require 'active_support/core_ext/string/inflections'
-require 'active_support/core_ext/string/conversions'
 
 module ActiveModel
   module Observing
diff --git a/activesupport/lib/active_support/core_ext/string/conversions.rb b/activesupport/lib/active_support/core_ext/string/conversions.rb
index cd7a42ed2bf10..6a243fe982000 100644
--- a/activesupport/lib/active_support/core_ext/string/conversions.rb
+++ b/activesupport/lib/active_support/core_ext/string/conversions.rb
@@ -47,15 +47,4 @@ def to_datetime
     d[5] += d.pop
     ::DateTime.civil(*d)
   end
-
-  # +constantize+ tries to find a declared constant with the name specified
-  # in the string. It raises a NameError when the name is not in CamelCase
-  # or is not initialized.
-  #
-  # Examples
-  #   "Module".constantize # => Module
-  #   "Class".constantize  # => Class
-  def constantize
-    ActiveSupport::Inflector.constantize(self)
-  end
 end
diff --git a/activesupport/lib/active_support/core_ext/string/inflections.rb b/activesupport/lib/active_support/core_ext/string/inflections.rb
index ef479d559e167..66c40347812fe 100644
--- a/activesupport/lib/active_support/core_ext/string/inflections.rb
+++ b/activesupport/lib/active_support/core_ext/string/inflections.rb
@@ -28,6 +28,17 @@ def singularize
     ActiveSupport::Inflector.singularize(self)
   end
 
+  # +constantize+ tries to find a declared constant with the name specified
+  # in the string. It raises a NameError when the name is not in CamelCase
+  # or is not initialized.
+  #
+  # Examples
+  #   "Module".constantize # => Module
+  #   "Class".constantize  # => Class
+  def constantize
+    ActiveSupport::Inflector.constantize(self)
+  end
+
   # By default, +camelize+ converts strings to UpperCamelCase. If the argument to camelize
   # is set to <tt>:lower</tt> then camelize produces lowerCamelCase.
   #