diff --git a/core/modules/field/tests/modules/field_test/field_test.install b/core/modules/field/tests/modules/field_test/field_test.install
index 1f8d848..1bb935c 100644
--- a/core/modules/field/tests/modules/field_test/field_test.install
+++ b/core/modules/field/tests/modules/field_test/field_test.install
@@ -129,6 +129,18 @@ function field_test_field_schema($field) {
     );
   }
   else {
+    $foreign_keys = array();
+    // The 'foreign keys' key is not always used in tests.
+    if (!empty($field['settings']['foreign_key_name'])) {
+      $foreign_keys['foreign keys'] = array(
+        // This is a dummy foreign key definition, references a table that
+        // doesn't exist, but that's not a problem.
+        $field['settings']['foreign_key_name'] => array(
+          'table' => $field['settings']['foreign_key_name'],
+          'columns' => array($field['settings']['foreign_key_name'] => 'id'),
+        ),
+      );
+    }
     return array(
       'columns' => array(
         'shape' => array(
@@ -142,14 +154,7 @@ function field_test_field_schema($field) {
           'not null' => FALSE,
         ),
       ),
-      'foreign keys' => array(
-        // This is a dummy foreign key definition, references a table that
-        // doesn't exist, but that's not a problem.
-        $field['settings']['foreign_key_name'] => array(
-          'table' => $field['settings']['foreign_key_name'],
-          'columns' => array($field['settings']['foreign_key_name'] => 'id'),
-        ),
-      ),
+      $foreign_keys,
     );
   }
 }