diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 1ba01d3618..3c0a766df6 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   PostgreSQL invalid `uuid` are convert to nil.
+
+    *Abdelkader Boudih*
+    
 *   Fix the schema dump generated for tables without constraints and with
     primary key with default value of custom PostgreSQL function result.
 
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/uuid.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/uuid.rb
index 89728b0fe2..dd97393eac 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/uuid.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/uuid.rb
@@ -3,12 +3,21 @@ module ActiveRecord
     module PostgreSQL
       module OID # :nodoc:
         class Uuid < Type::Value # :nodoc:
+          RFC_4122 = %r{\A\{?[a-fA-F0-9]{4}-?
+                             [a-fA-F0-9]{4}-?
+                             [a-fA-F0-9]{4}-?
+                             [1-5][a-fA-F0-9]{3}-?
+                             [8-Bab][a-fA-F0-9]{3}-?
+                             [a-fA-F0-9]{4}-?
+                             [a-fA-F0-9]{4}-?
+                             [a-fA-F0-9]{4}-?\}?\z}x
+
           def type
             :uuid
           end
 
           def type_cast(value)
-            value.presence
+            value.to_s[RFC_4122, 0]
           end
         end
       end
diff --git a/activerecord/test/cases/adapters/postgresql/uuid_test.rb b/activerecord/test/cases/adapters/postgresql/uuid_test.rb
index df8faff546..d7ff81a382 100644
--- a/activerecord/test/cases/adapters/postgresql/uuid_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/uuid_test.rb
@@ -60,6 +60,43 @@ class PostgresqlUUIDTest < ActiveRecord::TestCase
     assert_equal(nil, UUIDType.last.guid)
   end
 
+  def test_treat_invalid_uuid_as_nil
+    uuid = UUIDType.create! guid: 'foobar'
+    assert_equal(nil, uuid.guid)
+  end
+
+  def test_invalid_uuid_dont_modify_before_type_cast
+    uuid = UUIDType.new guid: 'foobar'
+    assert_equal 'foobar', uuid.guid_before_type_cast
+  end
+
+  def test_rfc_4122_regex
+    # Valid uuids
+    ['A0EEBC99-9C0B-4EF8-BB6D-6BB9BD380A11',
+     '{a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11}',
+     'a0eebc999c0b4ef8bb6d6bb9bd380a11',
+     'a0ee-bc99-9c0b-4ef8-bb6d-6bb9-bd38-0a11',
+     '{a0eebc99-9c0b4ef8-bb6d6bb9-bd380a11}'].each do |valid_uuid|
+      uuid = UUIDType.new guid: valid_uuid
+      assert_not_nil uuid.guid
+    end
+
+    # Invalid uuids
+    [['A0EEBC99-9C0B-4EF8-BB6D-6BB9BD380A11'],
+     Hash.new,
+     0,
+     0.0,
+     true,
+     'Z0000C99-9C0B-4EF8-BB6D-6BB9BD380A11',
+     '{a0eebc99-9c0b-4ef8-fb6d-6bb9bd380a11}',
+     'a0eebc999r0b4ef8ab6d6bb9bd380a11',
+     'a0ee-bc99------4ef8-bb6d-6bb9-bd38-0a11',
+     '{a0eebc99-bb6d6bb9-bd380a11}'].each do |invalid_uuid|
+      uuid = UUIDType.new guid: invalid_uuid
+      assert_nil uuid.guid
+    end
+  end
+
   def test_uuid_formats
     ["A0EEBC99-9C0B-4EF8-BB6D-6BB9BD380A11",
      "{a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11}",