diff --git a/src/contracts/FieldType/Indexable.php b/src/contracts/FieldType/Indexable.php
index 1d72714a9a..1229d34279 100644
--- a/src/contracts/FieldType/Indexable.php
+++ b/src/contracts/FieldType/Indexable.php
@@ -39,7 +39,7 @@ public function getIndexDefinition();
      * implementation of this interface), this method is used to define default
      * field for matching. Default field is typically used by Field criterion.
      *
-     * @return string
+     * @return string|null
      */
     public function getDefaultMatchField();
 
@@ -50,7 +50,7 @@ public function getDefaultMatchField();
      * implementation of this interface), this method is used to define default
      * field for sorting. Default field is typically used by Field sort clause.
      *
-     * @return string
+     * @return string|null
      */
     public function getDefaultSortField();
 }
diff --git a/src/lib/Search/Common/FieldNameResolver.php b/src/lib/Search/Common/FieldNameResolver.php
index 02a94ab5d2..1bce132395 100644
--- a/src/lib/Search/Common/FieldNameResolver.php
+++ b/src/lib/Search/Common/FieldNameResolver.php
@@ -263,6 +263,12 @@ public function getIndexFieldName(
         $indexDefinition = $indexFieldType->getIndexDefinition();
 
         // Should only happen by mistake, so let's throw if it does
+        if ($name === null) {
+            throw new RuntimeException(
+                "Undefined default sort or match field in '{$fieldTypeIdentifier}' Field Type's index definition"
+            );
+        }
+
         if (!isset($indexDefinition[$name])) {
             throw new RuntimeException(
                 "Could not find Field '{$name}' in '{$fieldTypeIdentifier}' Field Type's index definition"