diff --git a/lib/devise.rb b/lib/devise.rb
index 1b7e1df1..debd342b 100755
--- a/lib/devise.rb
+++ b/lib/devise.rb
@@ -294,6 +294,10 @@ module Devise
     Rails.gem_version >= Gem::Version.new("5.1.x")
   end
 
+  def self.activerecord51? # :nodoc:
+    defined?(ActiveRecord) && ActiveRecord.gem_version >= Gem::Version.new("5.1.x")
+  end
+
   # Default way to set up Devise. Run rails generate devise_install to create
   # a fresh initializer with all configuration values.
   def self.setup
diff --git a/lib/devise/models/confirmable.rb b/lib/devise/models/confirmable.rb
index 02ef6bc3..726b8fa9 100644
--- a/lib/devise/models/confirmable.rb
+++ b/lib/devise/models/confirmable.rb
@@ -253,7 +253,7 @@ module Devise
           generate_confirmation_token && save(validate: false)
         end
 
-        if Devise.rails51?
+        if Devise.activerecord51?
           def postpone_email_change_until_confirmation_and_regenerate_confirmation_token
             @reconfirmation_required = true
             self.unconfirmed_email = self.email
@@ -271,7 +271,7 @@ module Devise
           end
         end
 
-        if Devise.rails51?
+        if Devise.activerecord51?
           def postpone_email_change?
             postpone = self.class.reconfirmable &&
               will_save_change_to_email? &&
diff --git a/lib/devise/models/database_authenticatable.rb b/lib/devise/models/database_authenticatable.rb
index b1cdea22..a981b91a 100644
--- a/lib/devise/models/database_authenticatable.rb
+++ b/lib/devise/models/database_authenticatable.rb
@@ -137,7 +137,7 @@ module Devise
         encrypted_password[0,29] if encrypted_password
       end
 
-      if Devise.rails51?
+      if Devise.activerecord51?
         # Send notification to user when email changes.
         def send_email_changed_notification
           send_devise_notification(:email_changed, to: email_before_last_save)
@@ -165,7 +165,7 @@ module Devise
         Devise::Encryptor.digest(self.class, password)
       end
 
-      if Devise.rails51?
+      if Devise.activerecord51?
         def send_email_changed_notification?
           self.class.send_email_changed_notification && saved_change_to_email?
         end
@@ -175,7 +175,7 @@ module Devise
         end
       end
 
-      if Devise.rails51?
+      if Devise.activerecord51?
         def send_password_change_notification?
           self.class.send_password_change_notification && saved_change_to_encrypted_password?
         end
diff --git a/lib/devise/models/recoverable.rb b/lib/devise/models/recoverable.rb
index 75ca9cde..7857b686 100644
--- a/lib/devise/models/recoverable.rb
+++ b/lib/devise/models/recoverable.rb
@@ -97,7 +97,7 @@ module Devise
           send_devise_notification(:reset_password_instructions, token, {})
         end
 
-        if Devise.rails51?
+        if Devise.activerecord51?
           def clear_reset_password_token?
             encrypted_password_changed = respond_to?(:will_save_change_to_encrypted_password?) && will_save_change_to_encrypted_password?
             authentication_keys_changed = self.class.authentication_keys.any? do |attribute|
diff --git a/lib/devise/models/validatable.rb b/lib/devise/models/validatable.rb
index 761d76d8..7a397378 100644
--- a/lib/devise/models/validatable.rb
+++ b/lib/devise/models/validatable.rb
@@ -27,7 +27,7 @@ module Devise
 
         base.class_eval do
           validates_presence_of   :email, if: :email_required?
-          if Devise.rails51?
+          if Devise.activerecord51?
             validates_uniqueness_of :email, allow_blank: true, if: :will_save_change_to_email?
             validates_format_of     :email, with: email_regexp, allow_blank: true, if: :will_save_change_to_email?
           else