src/Context/FieldResolver.php | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/Context/FieldResolver.php b/src/Context/FieldResolver.php
index 453009d..fdb8932 100644
--- a/src/Context/FieldResolver.php
+++ b/src/Context/FieldResolver.php
@@ -6,6 +6,7 @@ use Drupal\Core\Entity\EntityFieldManagerInterface;
 use Drupal\Core\Entity\EntityTypeBundleInfoInterface;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\Entity\FieldableEntityInterface;
+use Drupal\Core\Entity\TypedData\EntityDataDefinitionInterface;
 use Drupal\Core\Field\TypedData\FieldItemDataDefinition;
 use Drupal\Core\TypedData\ComplexDataDefinitionInterface;
 use Drupal\Core\TypedData\DataReferenceDefinitionInterface;
@@ -376,8 +377,8 @@ class FieldResolver {
       $property_definitions = $definition->getPropertyDefinitions();
       foreach ($property_definitions as $property_name => $property_definition) {
         if ($property_definition instanceof DataReferenceDefinitionInterface) {
-          /* @var \Drupal\Core\Entity\TypedData\EntityDataDefinitionInterface $target_definition */
           $target_definition = $property_definition->getTargetDefinition();
+          assert($target_definition instanceof EntityDataDefinitionInterface, 'Entity reference fields should only be able to reference entities.');
           $reference_property_names[] = $property_name . ':' . $target_definition->getEntityTypeId();
         }
       }