diff --git a/CHANGELOG.md b/CHANGELOG.md
index d565111..3f4bc42 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+## [2.1.2] - 2020-03-16
+### Fixed
+- Related links must be allowed inside relationship documents (#104)
+
 ## [2.1.1] - 2019-12-19
 ### Fixed
 - ResourceIdentifier does not allow multiple meta members (#99)
@@ -22,7 +26,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Added
 - v2 initial release
 
-[Unreleased]: https://github.com/json-api-php/json-api/compare/2.1.1...HEAD
-[2.2.0]: https://github.com/json-api-php/json-api/compare/2.1.0...2.1.1
+[Unreleased]: https://github.com/json-api-php/json-api/compare/2.1.2...HEAD
+[2.1.2]: https://github.com/json-api-php/json-api/compare/2.1.1...2.1.2
+[2.1.1]: https://github.com/json-api-php/json-api/compare/2.1.0...2.1.1
 [2.1.0]: https://github.com/json-api-php/json-api/compare/2.0.1...2.1.0
 [2.0.1]: https://github.com/json-api-php/json-api/compare/2.0.0...2.0.1
diff --git a/composer.json b/composer.json
index 76bbb66..ffcd77e 100644
--- a/composer.json
+++ b/composer.json
@@ -13,7 +13,6 @@
   "require": {
     "php": ">=7.1",
     "ext-json": "*"
-
   },
   "require-dev": {
     "phpunit/phpunit": "^7.0||^8.0",
diff --git a/src/Internal/Identifier.php b/src/Internal/Identifier.php
index fa435a1..f8f9e47 100644
--- a/src/Internal/Identifier.php
+++ b/src/Internal/Identifier.php
@@ -8,8 +8,8 @@
 interface Identifier
 {
     /**
-     * @internal
      * @param array $registry
+     * @internal
      */
     public function registerIn(array &$registry): void;
 }
diff --git a/src/Link/RelatedLink.php b/src/Link/RelatedLink.php
index c1924ee..1def33c 100644
--- a/src/Link/RelatedLink.php
+++ b/src/Link/RelatedLink.php
@@ -3,10 +3,11 @@
 namespace JsonApiPhp\JsonApi\Link;
 
 use function JsonApiPhp\JsonApi\child;
+use JsonApiPhp\JsonApi\Internal\DataDocumentMember;
 use JsonApiPhp\JsonApi\Internal\LinkTrait;
 use JsonApiPhp\JsonApi\Internal\RelationshipMember;
 
-final class RelatedLink implements RelationshipMember
+final class RelatedLink implements RelationshipMember, DataDocumentMember
 {
     use LinkTrait;
 
diff --git a/src/PaginatedCollection.php b/src/PaginatedCollection.php
index 15e3cc7..e59c66f 100644
--- a/src/PaginatedCollection.php
+++ b/src/PaginatedCollection.php
@@ -33,8 +33,8 @@ public function attachTo($o): void
     }
 
     /**
-     * @internal
      * @param array $registry
+     * @internal
      */
     public function registerIn(array &$registry): void
     {
diff --git a/test/DataDocument/ManyResourceObjectsTest.php b/test/DataDocument/ManyResourceObjectsTest.php
index 3a2be82..54736e2 100644
--- a/test/DataDocument/ManyResourceObjectsTest.php
+++ b/test/DataDocument/ManyResourceObjectsTest.php
@@ -5,6 +5,7 @@
 use JsonApiPhp\JsonApi\Attribute;
 use JsonApiPhp\JsonApi\DataDocument;
 use JsonApiPhp\JsonApi\JsonApi;
+use JsonApiPhp\JsonApi\Link\RelatedLink;
 use JsonApiPhp\JsonApi\Link\SelfLink;
 use JsonApiPhp\JsonApi\Meta;
 use JsonApiPhp\JsonApi\ResourceCollection;
@@ -33,24 +34,23 @@ public function testExtendedDocument()
             '
             {
                 "data": [{
-                    "type": "apples",
+                    "type": "people",
                     "id": "1",
                     "attributes": {
-                        "color": "red",
-                        "sort": "Fuji"
+                        "name": "Martin Fowler"
                     },
                     "meta": {"apple_meta": "foo"}
                 },{
-                    "type": "apples",
+                    "type": "people",
                     "id": "2",
                     "attributes": {
-                        "color": "yellow",
-                        "sort": "Gala"
+                        "name": "Kent Beck"
                     },
                     "meta": {"apple_meta": "foo"}
                 }],
                 "links": {
-                    "self": "/apples"
+                    "self": "/books/123/relationships/authors",
+                    "related": "/books/123/authors"
                 },
                 "jsonapi": {
                     "version": "1.0"
@@ -61,21 +61,20 @@ public function testExtendedDocument()
             new DataDocument(
                 new ResourceCollection(
                     new ResourceObject(
-                        'apples',
+                        'people',
                         '1',
-                        new Attribute('color', 'red'),
-                        new Attribute('sort', 'Fuji'),
+                        new Attribute('name', 'Martin Fowler'),
                         new Meta('apple_meta', 'foo')
                     ),
                     new ResourceObject(
-                        'apples',
+                        'people',
                         '2',
-                        new Attribute('color', 'yellow'),
-                        new Attribute('sort', 'Gala'),
+                        new Attribute('name', 'Kent Beck'),
                         new Meta('apple_meta', 'foo')
                     )
                 ),
-                new SelfLink('/apples'),
+                new SelfLink('/books/123/relationships/authors'),
+                new RelatedLink('/books/123/authors'),
                 new JsonApi(),
                 new Meta('document_meta', 'bar')
             )
diff --git a/test/DataDocument/SingleResourceIdentifierTest.php b/test/DataDocument/SingleResourceIdentifierTest.php
index 1d12a77..165a625 100644
--- a/test/DataDocument/SingleResourceIdentifierTest.php
+++ b/test/DataDocument/SingleResourceIdentifierTest.php
@@ -4,6 +4,7 @@
 
 use JsonApiPhp\JsonApi\DataDocument;
 use JsonApiPhp\JsonApi\JsonApi;
+use JsonApiPhp\JsonApi\Link\RelatedLink;
 use JsonApiPhp\JsonApi\Link\SelfLink;
 use JsonApiPhp\JsonApi\Meta;
 use JsonApiPhp\JsonApi\ResourceIdentifier;
@@ -17,13 +18,13 @@ public function testMinimalDocument()
             '
             {
                 "data": {
-                    "type": "apples",
+                    "type": "companies",
                     "id": "1"
                 }
             }
             ',
             new DataDocument(
-                new ResourceIdentifier('apples', '1')
+                new ResourceIdentifier('companies', '1')
             )
         );
     }
@@ -34,7 +35,7 @@ public function testExtendedDocument()
             '
             {
                 "data": {
-                    "type": "apples",
+                    "type": "companies",
                     "id": "1",
                     "meta": {
                         "apple_meta": "foo", 
@@ -42,7 +43,8 @@ public function testExtendedDocument()
                     }
                 },
                 "links": {
-                    "self": "/apples/1"
+                    "self": "/books/123/relationships/publisher",
+                    "related": "/books/123/publisher"
                 },
                 "jsonapi": {
                     "version": "1.0"
@@ -52,12 +54,13 @@ public function testExtendedDocument()
             ',
             new DataDocument(
                 new ResourceIdentifier(
-                    'apples',
+                    'companies',
                     '1',
                     new Meta('apple_meta', 'foo'),
                     new Meta('bar', [42])
                 ),
-                new SelfLink('/apples/1'),
+                new SelfLink('/books/123/relationships/publisher'),
+                new RelatedLink('/books/123/publisher'),
                 new JsonApi(),
                 new Meta('document_meta', 'bar')
             )