diff --git a/activerecord/lib/active_record/nested_attributes.rb b/activerecord/lib/active_record/nested_attributes.rb
index e3122d1..1b7f0c6 100644
--- a/activerecord/lib/active_record/nested_attributes.rb
+++ b/activerecord/lib/active_record/nested_attributes.rb
@@ -227,11 +227,18 @@ module ActiveRecord
       marked_for_destruction?
     end
 
+    # See ActionView::Helpers::FormHelper::fields_for for more info.
+    def _unlink
+      # TODO: should return true when validation of a form fails and
+      # a record has been marked for unlinking.
+      false
+    end
+
     private
 
     # Attribute hash keys that should not be assigned as normal attributes.
     # These hash keys are nested attributes implementation details.
-    UNASSIGNABLE_KEYS = %w{ id _delete }
+    UNASSIGNABLE_KEYS = %w{ id _delete _unlink }
 
     # Assigns the given attributes to the association.
     #
@@ -297,8 +304,19 @@ module ActiveRecord
           unless reject_new_record?(association_name, attributes)
             send(association_name).build(attributes.except(*UNASSIGNABLE_KEYS))
           end
-        elsif existing_record = send(association_name).detect { |record| record.id.to_s == attributes['id'].to_s }
-          assign_to_or_mark_for_destruction(existing_record, attributes, allow_destroy)
+        else
+          existing_record = send(association_name).detect { |record| record.id.to_s == attributes['id'].to_s }
+          if attributes.has_key?("_unlink")
+            # here :autosave doesn't work as I would have expected
+            if has_unlink_flag?(attributes)
+              send(association_name).delete(existing_record)
+            elsif existing_record.nil?
+              existing_record = self.class.reflections[association_name].klass.find(attributes['id'].to_s.to_i)
+              send(association_name).push(existing_record) if existing_record
+            end
+          elsif existing_record
+            assign_to_or_mark_for_destruction(existing_record, attributes, allow_destroy)
+          end
         end
       end
     end
@@ -318,11 +336,17 @@ module ActiveRecord
       ConnectionAdapters::Column.value_to_boolean hash['_delete']
     end
 
+    # Determines if a hash contains a truthy _unlink key.
+    def has_unlink_flag?(hash)
+      ConnectionAdapters::Column.value_to_boolean hash['_unlink']
+    end
+
     # Determines if a new record should be build by checking for
-    # has_delete_flag? or if a <tt>:reject_if</tt> proc exists for this
-    # association and evaluates to +true+.
+    # has_delete_flag? or has_unlink_flag? or if a <tt>:reject_if</tt> proc
+    # exists for this association and evaluates to +true+.
     def reject_new_record?(association_name, attributes)
       has_delete_flag?(attributes) ||
+      has_unlink_flag?(attributes) ||
         self.class.reject_new_nested_attributes_procs[association_name].try(:call, attributes)
     end
   end