diff --git a/addon/serializers/rest.js b/addon/serializers/rest.js
index f10533fd614..fa3dc9e756c 100644
--- a/addon/serializers/rest.js
+++ b/addon/serializers/rest.js
@@ -762,24 +762,6 @@ const RESTSerializer = JSONSerializer.extend({
     let typeKey = this.keyForPolymorphicType(key, relationship.type, 'serialize');
     let belongsTo = snapshot.belongsTo(key);
 
-    // old way of getting the key for the polymorphic type
-    key = this.keyForAttribute ? this.keyForAttribute(key, "serialize") : key;
-    key = `${key}Type`;
-
-    // The old way of serializing the type of a polymorphic record used
-    // `keyForAttribute`, which is not correct. The next code checks if the old
-    // way is used and if it differs from the new way of using
-    // `keyForPolymorphicType`. If this is the case, a deprecation warning is
-    // logged and the old way is restored (so nothing breaks).
-    if (key !== typeKey && this.keyForPolymorphicType === RESTSerializer.prototype.keyForPolymorphicType) {
-      deprecate("The key to serialize the type of a polymorphic record is created via keyForAttribute which has been deprecated. Use the keyForPolymorphicType hook instead.", false, {
-        id: 'ds.rest-serializer.deprecated-key-for-polymorphic-type',
-        until: '3.0.0'
-      });
-
-      typeKey = key;
-    }
-
     if (isNone(belongsTo)) {
       json[typeKey] = null;
     } else {
diff --git a/tests/integration/serializers/rest-serializer-test.js b/tests/integration/serializers/rest-serializer-test.js
index f2aca2c68ae..8516c28d9e5 100644
--- a/tests/integration/serializers/rest-serializer-test.js
+++ b/tests/integration/serializers/rest-serializer-test.js
@@ -573,27 +573,6 @@ test('serializeBelongsTo with async polymorphic', function(assert) {
   assert.deepEqual(json, expected, 'returned JSON is correct');
 });
 
-testInDebug('serializeBelongsTo logs deprecation when old behavior for getting polymorphic type key is used', function(assert) {
-  var evilMinion, doomsdayDevice;
-  var json = {};
-  var expected = { evilMinion: '1', myCustomKeyType: 'evilMinion' };
-
-  env.restSerializer.keyForAttribute = function() {
-    return 'myCustomKey';
-  };
-
-  run(function() {
-    evilMinion = env.store.createRecord('evil-minion', { id: 1, name: 'Tomster' });
-    doomsdayDevice = env.store.createRecord('doomsday-device', { id: 2, name: 'Yehuda', evilMinion: evilMinion });
-  });
-
-  assert.expectDeprecation(function() {
-    env.restSerializer.serializeBelongsTo(doomsdayDevice._createSnapshot(), json, { key: 'evilMinion', options: { polymorphic: true, async: true } });
-  }, "The key to serialize the type of a polymorphic record is created via keyForAttribute which has been deprecated. Use the keyForPolymorphicType hook instead.");
-
-  assert.deepEqual(json, expected, 'returned JSON is correct');
-});
-
 test('keyForPolymorphicType can be used to overwrite how the type of a polymorphic record is serialized', function(assert) {
   var evilMinion, doomsdayDevice;
   var json = {};