src/ResourceType/ResourceType.php              | 4 +++-
 tests/src/Functional/JsonApiRegressionTest.php | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/ResourceType/ResourceType.php b/src/ResourceType/ResourceType.php
index 33d7d75..e0c20a3 100644
--- a/src/ResourceType/ResourceType.php
+++ b/src/ResourceType/ResourceType.php
@@ -267,7 +267,9 @@ class ResourceType {
     $this->isLocatable = $is_locatable;
     $this->isMutable = $is_mutable;
 
-    $this->typeName = sprintf('%s--%s', $this->entityTypeId, $this->bundle);
+    $this->typeName = $this->bundle === '?'
+      ? 'unknown'
+      : sprintf('%s--%s', $this->entityTypeId, $this->bundle);
 
     $this->disabledFields = array_keys(array_filter($field_mapping, function ($v) {
       return $v === FALSE;
diff --git a/tests/src/Functional/JsonApiRegressionTest.php b/tests/src/Functional/JsonApiRegressionTest.php
index 6a91f4d..c579fda 100644
--- a/tests/src/Functional/JsonApiRegressionTest.php
+++ b/tests/src/Functional/JsonApiRegressionTest.php
@@ -417,7 +417,7 @@ class JsonApiRegressionTest extends JsonApiFunctionalTestBase {
     // resource type is NOT deduced.
     $this->assertSame([
       [
-        'type' => 'node--?',
+        'type' => 'unknown',
         'id' => 'missing',
         'meta' => [
           'links' => [