diff --git a/lib/extensions/has_one.rb b/lib/extensions/has_one.rb
index 4e1ef25..0bd134c 100644
--- a/lib/extensions/has_one.rb
+++ b/lib/extensions/has_one.rb
@@ -1,16 +1,20 @@
-require 'active_record'
+begin
+  require 'active_record'
 
-::ActiveRecord::Associations::Builder::HasOne.class_eval do
-  # Based on
-  # https://github.com/rails/rails/blob/master/activerecord/lib/active_record/associations/builder/collection_association.rb#L50
-  # https://github.com/rails/rails/blob/master/activerecord/lib/active_record/associations/builder/singular_association.rb#L11
-  def self.define_accessors(mixin, reflection)
-    super
-    name = reflection.name
-    mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
-      def #{name.to_s}_id
-        association(:#{name}).reader.try(:id)
-      end
-    CODE
+  ::ActiveRecord::Associations::Builder::HasOne.class_eval do
+    # Based on
+    # https://github.com/rails/rails/blob/master/activerecord/lib/active_record/associations/builder/collection_association.rb#L50
+    # https://github.com/rails/rails/blob/master/activerecord/lib/active_record/associations/builder/singular_association.rb#L11
+    def self.define_accessors(mixin, reflection)
+      super
+      name = reflection.name
+      mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
+        def #{name.to_s}_id
+          association(:#{name}).reader.try(:id)
+        end
+      CODE
+    end
   end
+rescue LoadError
+  # active_record can't be loaded so we shouldn't try to monkey-patch it.
 end