diff --git a/lib/deserializer-utils.js b/lib/deserializer-utils.js
index 1265fd4..adc35eb 100644
--- a/lib/deserializer-utils.js
+++ b/lib/deserializer-utils.js
@@ -36,7 +36,7 @@ module.exports = function (jsonapi, data, opts) {
       if (included) {
         // To prevent circular references, check if the record type
         // has already been processed in this thread
-        if (ancestry.indexOf(included.type) > -1) {
+        if (ancestry.find((aIncluded) => aIncluded === included.type)) {
           return Promise
             .all([extractAttributes(included)])
             .then(function (results) {
@@ -47,7 +47,7 @@ module.exports = function (jsonapi, data, opts) {
         }
 
         return Promise
-          .all([extractAttributes(included), extractRelationships(included, ancestry + ':' + included.type + included.id)])
+          .all([extractAttributes(included), extractRelationships(included, [...ancestry, included.type])])
           .then(function (results) {
             var attributes = results[0];
             var relationships = results[1];
@@ -146,7 +146,7 @@ module.exports = function (jsonapi, data, opts) {
 
   this.perform = function () {
     return Promise
-      .all([extractAttributes(data), extractRelationships(data, data.type + data.id)])
+      .all([extractAttributes(data), extractRelationships(data, [data.type])])
       .then(function (results) {
         var attributes = results[0];
         var relationships = results[1];
diff --git a/package-lock.json b/package-lock.json
index 8b76b04..5fa975e 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "jsonapi-serializer",
-  "version": "3.6.3",
+  "version": "3.6.6",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
@@ -1289,7 +1289,8 @@
         "ansi-regex": {
           "version": "2.1.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "aproba": {
           "version": "1.2.0",
@@ -1310,12 +1311,14 @@
         "balanced-match": {
           "version": "1.0.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "brace-expansion": {
           "version": "1.1.11",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "balanced-match": "^1.0.0",
             "concat-map": "0.0.1"
@@ -1330,17 +1333,20 @@
         "code-point-at": {
           "version": "1.1.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "concat-map": {
           "version": "0.0.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "console-control-strings": {
           "version": "1.1.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "core-util-is": {
           "version": "1.0.2",
@@ -1457,7 +1463,8 @@
         "inherits": {
           "version": "2.0.3",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "ini": {
           "version": "1.3.5",
@@ -1469,6 +1476,7 @@
           "version": "1.0.0",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "number-is-nan": "^1.0.0"
           }
@@ -1483,6 +1491,7 @@
           "version": "3.0.4",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "brace-expansion": "^1.1.7"
           }
@@ -1490,12 +1499,14 @@
         "minimist": {
           "version": "0.0.8",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "minipass": {
           "version": "2.2.4",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "safe-buffer": "^5.1.1",
             "yallist": "^3.0.0"
@@ -1514,6 +1525,7 @@
           "version": "0.5.1",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "minimist": "0.0.8"
           }
@@ -1594,7 +1606,8 @@
         "number-is-nan": {
           "version": "1.0.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "object-assign": {
           "version": "4.1.1",
@@ -1606,6 +1619,7 @@
           "version": "1.4.0",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "wrappy": "1"
           }
@@ -1691,7 +1705,8 @@
         "safe-buffer": {
           "version": "5.1.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "safer-buffer": {
           "version": "2.1.2",
@@ -1727,6 +1742,7 @@
           "version": "1.0.2",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "code-point-at": "^1.0.0",
             "is-fullwidth-code-point": "^1.0.0",
@@ -1746,6 +1762,7 @@
           "version": "3.0.1",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "ansi-regex": "^2.0.0"
           }
@@ -1789,12 +1806,14 @@
         "wrappy": {
           "version": "1.0.2",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "yallist": {
           "version": "3.0.2",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         }
       }
     },