diff --git a/src/Entity/Facet.php b/src/Entity/Facet.php
index 848713d..a085542 100644
--- a/src/Entity/Facet.php
+++ b/src/Entity/Facet.php
@@ -3,6 +3,7 @@
 namespace Drupal\facets\Entity;
 
 use Drupal\Core\Config\Entity\ConfigEntityBase;
+use Drupal\facets\Exception\Exception;
 use Drupal\facets\FacetInterface;
 
 /**
@@ -534,6 +535,10 @@ class Facet extends ConfigEntityBase implements FacetInterface {
       return $this->facetSourceConfig;
     }
 
+    if (empty($this->facet_source_id)) {
+      throw new Exception("WAT? {$this->facet_source_id}");
+    }
+
     // We didn't have a facet source config entity yet for this facet source
     // plugin, so we create it on the fly.
     $facet_source = new FacetSource(