diff --git a/core/modules/jsonapi/src/ResourceType/ResourceType.php b/core/modules/jsonapi/src/ResourceType/ResourceType.php
index 955feff354..549999d899 100644
--- a/core/modules/jsonapi/src/ResourceType/ResourceType.php
+++ b/core/modules/jsonapi/src/ResourceType/ResourceType.php
@@ -37,12 +37,25 @@ class ResourceType {
   protected $bundle;
 
   /**
-   * The type name.
+   * The type name (mutable).
+   *
+   * This value can be overridden by JSON:API Extras or any other
+   * custom solution that alters the "createResourceType()" method
+   * of "jsonapi_extras.resource_type.repository" service.
    *
    * @var string
    */
   protected $typeName;
 
+  /**
+   * The type name (immutable).
+   *
+   * The name of a resource in the "ENTITY_TYPE_ID--ENTITY_BUNDLE" format.
+   *
+   * @var string
+   */
+  private $typeNameInternal;
+
   /**
    * The class to which a payload converts to.
    *
@@ -112,7 +125,7 @@ public function getEntityTypeId() {
   }
 
   /**
-   * Gets the type name.
+   * Gets the type name (mutable).
    *
    * @return string
    *   The type name.
@@ -121,6 +134,16 @@ public function getTypeName() {
     return $this->typeName;
   }
 
+  /**
+   * Gets the type name (immutable).
+   *
+   * @return string
+   *   The type name.
+   */
+  public function getTypeNameInternal() {
+    return $this->typeNameInternal;
+  }
+
   /**
    * Gets the bundle.
    *
@@ -356,7 +379,7 @@ public function __construct($entity_type_id, $bundle, $deserialization_target_cl
     $this->isVersionable = $is_versionable;
     $this->fields = $fields;
 
-    $this->typeName = $this->bundle === '?'
+    $this->typeNameInternal = $this->typeName = $this->bundle === '?'
       ? 'unknown'
       : sprintf('%s--%s', $this->entityTypeId, $this->bundle);
 
@@ -397,11 +420,12 @@ public function setRelatableResourceTypes(array $relatable_resource_types) {
    */
   public function getRelatableResourceTypes() {
     if (!isset($this->relatableResourceTypesByField)) {
-      $this->relatableResourceTypesByField = array_reduce(array_map(function (ResourceTypeRelationship $field) {
-        return [$field->getPublicName() => $field->getRelatableResourceTypes()];
-      }, array_filter($this->fields, function (ResourceTypeField $field) {
-        return $field instanceof ResourceTypeRelationship;
-      })), 'array_merge', []);
+      $this->relatableResourceTypesByField = [];
+      foreach ($this->fields as $field) {
+        if ($field instanceof ResourceTypeRelationship) {
+          $this->relatableResourceTypesByField[$field->getPublicName()] = $field->getRelatableResourceTypes();
+        }
+      }
     }
     return $this->relatableResourceTypesByField;
   }
diff --git a/core/modules/jsonapi/src/ResourceType/ResourceTypeRelationship.php b/core/modules/jsonapi/src/ResourceType/ResourceTypeRelationship.php
index 8e782a527c..b1a9b4fc98 100644
--- a/core/modules/jsonapi/src/ResourceType/ResourceTypeRelationship.php
+++ b/core/modules/jsonapi/src/ResourceType/ResourceTypeRelationship.php
@@ -2,6 +2,8 @@
 
 namespace Drupal\jsonapi\ResourceType;
 
+use Drupal\Component\Assertion\Inspector;
+
 /**
  * Specialization of a ResourceTypeField to represent a resource relationship.
  *
@@ -32,6 +34,7 @@ class ResourceTypeRelationship extends ResourceTypeField {
    *   A new instance of the field with the given relatable resource types.
    */
   public function withRelatableResourceTypes(array $resource_types) {
+    assert(Inspector::assertAllObjects($resource_types, ResourceType::class));
     $relationship = new static($this->internalName, $this->publicName, $this->enabled, $this->hasOne);
     $relationship->relatableResourceTypes = $resource_types;
     return $relationship;
diff --git a/core/modules/jsonapi/src/ResourceType/ResourceTypeRepository.php b/core/modules/jsonapi/src/ResourceType/ResourceTypeRepository.php
index 724264732f..8824362fb1 100644
--- a/core/modules/jsonapi/src/ResourceType/ResourceTypeRepository.php
+++ b/core/modules/jsonapi/src/ResourceType/ResourceTypeRepository.php
@@ -124,7 +124,7 @@ public function all() {
         $resource_types = array_reduce($bundles, function ($resource_types, $bundle) use ($entity_type) {
           $resource_type = $this->createResourceType($entity_type, (string) $bundle);
           return array_merge($resource_types, [
-            $resource_type->getTypeName() => $resource_type,
+            $resource_type->getTypeNameInternal() => $resource_type,
           ]);
         }, $resource_types);
       }
diff --git a/core/modules/jsonapi/tests/modules/jsonapi_test_resource_typename_hack/jsonapi_test_resource_typename_hack.info.yml b/core/modules/jsonapi/tests/modules/jsonapi_test_resource_typename_hack/jsonapi_test_resource_typename_hack.info.yml
new file mode 100644
index 0000000000..1323700898
--- /dev/null
+++ b/core/modules/jsonapi/tests/modules/jsonapi_test_resource_typename_hack/jsonapi_test_resource_typename_hack.info.yml
@@ -0,0 +1,4 @@
+name: 'JSON:API test resource typeName override'
+type: module
+package: Testing
+core: 8.x
diff --git a/core/modules/jsonapi/tests/modules/jsonapi_test_resource_typename_hack/jsonapi_test_resource_typename_hack.services.yml b/core/modules/jsonapi/tests/modules/jsonapi_test_resource_typename_hack/jsonapi_test_resource_typename_hack.services.yml
new file mode 100644
index 0000000000..2238b13a6d
--- /dev/null
+++ b/core/modules/jsonapi/tests/modules/jsonapi_test_resource_typename_hack/jsonapi_test_resource_typename_hack.services.yml
@@ -0,0 +1,5 @@
+services:
+  Drupal\jsonapi_test_resource_typename_hack\ResourceType\ResourceTypeRepository:
+    decorates: jsonapi.resource_type.repository
+    parent: jsonapi.resource_type.repository
+    public: false
diff --git a/core/modules/jsonapi/tests/modules/jsonapi_test_resource_typename_hack/src/ResourceType/ResourceType.php b/core/modules/jsonapi/tests/modules/jsonapi_test_resource_typename_hack/src/ResourceType/ResourceType.php
new file mode 100644
index 0000000000..1d68da3fe5
--- /dev/null
+++ b/core/modules/jsonapi/tests/modules/jsonapi_test_resource_typename_hack/src/ResourceType/ResourceType.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace Drupal\jsonapi_test_resource_typename_hack\ResourceType;
+
+use Drupal\jsonapi\ResourceType\ResourceType as ResourceTypeBase;
+
+/**
+ * Custom resource type.
+ */
+class ResourceType extends ResourceTypeBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function __construct(...$arguments) {
+    parent::__construct(...$arguments);
+    // That's what JSON:API Extras allows to do.
+    $this->typeName = str_replace('--', '==', $this->typeName);
+  }
+
+}
diff --git a/core/modules/jsonapi/tests/modules/jsonapi_test_resource_typename_hack/src/ResourceType/ResourceTypeRepository.php b/core/modules/jsonapi/tests/modules/jsonapi_test_resource_typename_hack/src/ResourceType/ResourceTypeRepository.php
new file mode 100644
index 0000000000..2da8d7b326
--- /dev/null
+++ b/core/modules/jsonapi/tests/modules/jsonapi_test_resource_typename_hack/src/ResourceType/ResourceTypeRepository.php
@@ -0,0 +1,29 @@
+<?php
+
+namespace Drupal\jsonapi_test_resource_typename_hack\ResourceType;
+
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\jsonapi\ResourceType\ResourceTypeRepository as ResourceTypeRepositoryBase;
+
+/**
+ * Provides a repository of JSON:API resource types.
+ */
+class ResourceTypeRepository extends ResourceTypeRepositoryBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function createResourceType(EntityTypeInterface $entity_type, $bundle) {
+    return new ResourceType(
+      $entity_type->id(),
+      $bundle,
+      $entity_type->getClass(),
+      $entity_type->isInternal(),
+      static::isLocatableResourceType($entity_type, $bundle),
+      static::isMutableResourceType($entity_type, $bundle),
+      static::isVersionableResourceType($entity_type),
+      static::getFields($this->getAllFieldNames($entity_type, $bundle), $entity_type, $bundle)
+    );
+  }
+
+}
diff --git a/core/modules/jsonapi/tests/src/Kernel/ResourceType/ResourceTypeRepositoryTypeNameHackTest.php b/core/modules/jsonapi/tests/src/Kernel/ResourceType/ResourceTypeRepositoryTypeNameHackTest.php
new file mode 100644
index 0000000000..6bd77a84b3
--- /dev/null
+++ b/core/modules/jsonapi/tests/src/Kernel/ResourceType/ResourceTypeRepositoryTypeNameHackTest.php
@@ -0,0 +1,71 @@
+<?php
+
+namespace Drupal\Tests\jsonapi\Kernel\ResourceType;
+
+use Drupal\jsonapi\ResourceType\ResourceType;
+use Drupal\Tests\jsonapi\Kernel\JsonapiKernelTestBase;
+
+/**
+ * @coversDefaultClass \Drupal\jsonapi\ResourceType\ResourceTypeRepository
+ * @group jsonapi
+ *
+ * @internal
+ */
+class ResourceTypeRepositoryTypeNameHackTest extends JsonapiKernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = [
+    'node',
+    'user',
+    'system',
+    'serialization',
+    'jsonapi_test_resource_typename_hack',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->container
+      ->get('entity_type.manager')
+      ->getStorage('node_type')
+      ->create(['type' => 'page'])
+      ->save();
+  }
+
+  /**
+   * Ensures resource repository forms the listing using internal names.
+   *
+   * JSON:API Extras is used widely and it's hard to imagine how big its
+   * coverage at existing projects. The project allows renaming resource
+   * types (e.g. "user---user" to "user") and this negatively affects the
+   * operability of JSON:API itself.
+   *
+   * @link https://www.drupal.org/project/drupal/issues/2996114
+   */
+  public function test() {
+    $repository = $this->container->get('jsonapi.resource_type.repository');
+
+    static::assertInstanceOf(ResourceType::class, $repository->get('user', 'user'));
+    static::assertInstanceOf(ResourceType::class, $repository->getByTypeName('node--page'));
+
+    foreach ($repository->all() as $id => $resource_type) {
+      static::assertSame(
+        sprintf('%s--%s', $resource_type->getEntityTypeId(), $resource_type->getBundle()),
+        $id,
+        'The key must always be in the "ENTITY_TYPE_ID--ENTITY_BUNDLE" format.'
+      );
+
+      static::assertNotSame(
+        $resource_type->getTypeName(),
+        $id,
+        'The type name can be changed and not always is the same as the internal type name.'
+      );
+    }
+  }
+
+}