2 files changed, 16 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/autosave_association.rb b/activerecord/lib/active_record/autosave_association.rb
index 0792d19c3e..5f38bd51f6 100644
--- a/activerecord/lib/active_record/autosave_association.rb
+++ b/activerecord/lib/active_record/autosave_association.rb
@@ -222,6 +222,7 @@ module ActiveRecord
               true
             end
             validate validation_method
+            after_validation :_ensure_no_duplicate_errors
           end
         end
     end
@@ -456,5 +457,11 @@ module ActiveRecord
           end
         end
       end
+
+      def _ensure_no_duplicate_errors
+        errors.messages.each_key do |attribute|
+          errors[attribute].uniq!
+        end
+      end
   end
 end
diff --git a/activerecord/lib/active_record/nested_attributes.rb b/activerecord/lib/active_record/nested_attributes.rb
index c942d0e265..a6b76b25bf 100644
--- a/activerecord/lib/active_record/nested_attributes.rb
+++ b/activerecord/lib/active_record/nested_attributes.rb
@@ -386,6 +386,9 @@ module ActiveRecord
     # then the existing record will be marked for destruction.
     def assign_nested_attributes_for_one_to_one_association(association_name, attributes)
       options = self.nested_attributes_options[association_name]
+      if attributes.respond_to?(:permitted?)
+        attributes = attributes.to_h
+      end
       attributes = attributes.with_indifferent_access
       existing_record = send(association_name)
 
@@ -442,6 +445,9 @@ module ActiveRecord
     #   ])
     def assign_nested_attributes_for_collection_association(association_name, attributes_collection)
       options = self.nested_attributes_options[association_name]
+      if attributes_collection.respond_to?(:permitted?)
+        attributes_collection = attributes_collection.to_h
+      end
 
       unless attributes_collection.is_a?(Hash) || attributes_collection.is_a?(Array)
         raise ArgumentError, "Hash or Array expected, got #{attributes_collection.class.name} (#{attributes_collection.inspect})"
@@ -468,6 +474,9 @@ module ActiveRecord
       end
 
       attributes_collection.each do |attributes|
+        if attributes.respond_to?(:permitted?)
+          attributes = attributes.to_h
+        end
         attributes = attributes.with_indifferent_access
 
         if attributes['id'].blank?