diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 44ddbbcf77..956d43de1c 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,21 @@
+*   Allow composite primary key to be derived from schema
+
+    Booting an application with a schema that contains composite primary keys
+    will not issue warning and won't `nil`ify the `ActiveRecord::Base#primary_key` value anymore.
+
+    Given a `travel_routes` table definition and a `TravelRoute` model like:
+    ```ruby
+    create_table :travel_routes, primary_key: [:origin, :destination], force: true do |t|
+      t.string :origin
+      t.string :destination
+    end
+
+    class TravelRoute < ActiveRecord::Base; end
+    ```
+    The `TravelRoute.primary_key` value will be automatically derived to `["origin", "destination"]`
+
+    *Nikita Vasilevsky*
+
 *   Include the `connection_pool` with exceptions raised from an adapter.
 
     The `connection_pool` provides added context such as the connection used
diff --git a/activerecord/lib/active_record/attribute_methods/primary_key.rb b/activerecord/lib/active_record/attribute_methods/primary_key.rb
index 0dc792f452..63759ad462 100644
--- a/activerecord/lib/active_record/attribute_methods/primary_key.rb
+++ b/activerecord/lib/active_record/attribute_methods/primary_key.rb
@@ -133,8 +133,7 @@ def get_primary_key(base_name) # :nodoc:
               base_name.foreign_key
             else
               if ActiveRecord::Base != self && table_exists?
-                pk = connection.schema_cache.primary_keys(table_name)
-                suppress_composite_primary_key(pk)
+                connection.schema_cache.primary_keys(table_name)
               else
                 "id"
               end
@@ -178,16 +177,6 @@ def inherited(base)
                 @quoted_primary_key = nil
               end
             end
-
-            def suppress_composite_primary_key(pk)
-              return pk unless pk.is_a?(Array)
-
-              warn <<~WARNING
-                WARNING: Active Record does not support composite primary key.
-
-                #{table_name} has composite primary key. Composite primary key is ignored.
-              WARNING
-            end
         end
     end
   end
diff --git a/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb b/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
index 2cfead5b98..96d68feff2 100644
--- a/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
@@ -166,19 +166,6 @@ def test_proper_usage_of_primary_keys_and_join_table
     assert_equal 1, country.treaties.count
   end
 
-  def test_join_table_composite_primary_key_should_not_warn
-    country = Country.new(name: "India")
-    country.country_id = "c1"
-    country.save!
-
-    treaty = Treaty.new(name: "peace")
-    treaty.treaty_id = "t1"
-    warning = capture(:stderr) do
-      country.treaties << treaty
-    end
-    assert_no_match(/WARNING: Active Record does not support composite primary key\./, warning)
-  end
-
   def test_has_and_belongs_to_many
     david = Developer.find(1)
 
diff --git a/activerecord/test/cases/primary_keys_test.rb b/activerecord/test/cases/primary_keys_test.rb
index 7f2f3f03e7..36411593cd 100644
--- a/activerecord/test/cases/primary_keys_test.rb
+++ b/activerecord/test/cases/primary_keys_test.rb
@@ -463,16 +463,16 @@ def test_id_predicate_composite
     end
   end
 
-  def test_primary_key_issues_warning
-    model = Class.new(ActiveRecord::Base) do
-      def self.table_name
-        "uber_barcodes"
+  def test_derives_composite_primary_key
+    def test_primary_key_issues_warning
+      model = Class.new(ActiveRecord::Base) do
+        def self.table_name
+          "uber_barcodes"
+        end
       end
+
+      assert_equal ["region", "code"], model.primary_key
     end
-    warning = capture(:stderr) do
-      assert_nil model.primary_key
-    end
-    assert_match(/WARNING: Active Record does not support composite primary key\./, warning)
   end
 
   def test_collectly_dump_composite_primary_key
diff --git a/activerecord/test/models/cpk/book.rb b/activerecord/test/models/cpk/book.rb
index cdfde3bfd3..7208c70c06 100644
--- a/activerecord/test/models/cpk/book.rb
+++ b/activerecord/test/models/cpk/book.rb
@@ -3,7 +3,6 @@
 module Cpk
   class Book < ActiveRecord::Base
     self.table_name = :cpk_books
-    self.primary_key = [:author_id, :number]
 
     belongs_to :order, autosave: true, query_constraints: [:shop_id, :order_id]
     belongs_to :author, class_name: "Cpk::Author"
diff --git a/activerecord/test/models/cpk/order.rb b/activerecord/test/models/cpk/order.rb
index d1b7d6375a..6fc5a326a8 100644
--- a/activerecord/test/models/cpk/order.rb
+++ b/activerecord/test/models/cpk/order.rb
@@ -3,6 +3,8 @@
 module Cpk
   class Order < ActiveRecord::Base
     self.table_name = :cpk_orders
+    # explicit definition is to allow schema definition to be simplified
+    # to be shared between different databases
     self.primary_key = [:shop_id, :id]
 
     has_many :order_agreements, primary_key: :id