2 files changed, 12 insertions, 7 deletions
diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index e5b3af8252..278c95e27b 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -309,15 +309,12 @@ module ActiveRecord
       def replace_on_target(record, index, skip_callbacks)
         callback(:before_add, record) unless skip_callbacks
 
-        was_loaded = loaded?
         yield(record) if block_given?
 
-        unless !was_loaded && loaded?
-          if index
-            @target[index] = record
-          else
-            @target << record
-          end
+        if index
+          @target[index] = record
+        else
+          append_record(record)
         end
 
         callback(:after_add, record) unless skip_callbacks
@@ -514,6 +511,10 @@ module ActiveRecord
             load_target.select { |r| ids.include?(r.id.to_s) }
           end
         end
+
+        def append_record(record)
+          @target << record unless @target.include?(record)
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index d258eac0ed..1f264d325a 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -203,6 +203,10 @@ module ActiveRecord
         def invertible_for?(record)
           false
         end
+
+        def append_record(record)
+          @target << record
+        end
     end
   end
 end