diff --git a/lib/devise/models/validatable.rb b/lib/devise/models/validatable.rb
index 1c22fb5fec..29a1ce3ce5 100644
--- a/lib/devise/models/validatable.rb
+++ b/lib/devise/models/validatable.rb
@@ -34,7 +34,7 @@ def self.included(base)
 
           validates_presence_of     :password, if: :password_required?
           validates_confirmation_of :password, if: :password_required?
-          validates_length_of       :password, within: password_length, allow_blank: true
+          validates_length_of(:password, within: password_length, allow_blank: true) if password_length
         end
       end