diff --git a/activerecord/lib/active_record/nested_attributes.rb b/activerecord/lib/active_record/nested_attributes.rb
index 8a2a06f2ca347..0f9b52f69f184 100644
--- a/activerecord/lib/active_record/nested_attributes.rb
+++ b/activerecord/lib/active_record/nested_attributes.rb
@@ -81,6 +81,9 @@ class TooManyRecords < ActiveRecordError
     #
     # Note that the model will _not_ be destroyed until the parent is saved.
     #
+    # Also note that the model will not be destroyed unless you also specify
+    # its id in the updated hash. 
+    #
     # === One-to-many
     #
     # Consider a member that has a number of posts: