--- a/src/FacetManager/DefaultFacetManager.php
+++ b/src/FacetManager/DefaultFacetManager.php
@@ -511,29 +511,48 @@
    *   A sorted array of results.
    */
   protected function sortFacetResults(array $active_sort_processors, array $results) {
-    uasort($results, function ($a, $b) use ($active_sort_processors) {
-      $return = 0;
-      foreach ($active_sort_processors as $sort_processor) {
-        if ($return = $sort_processor->sortResults($a, $b)) {
-          if ($sort_processor->getConfiguration()['sort'] == 'DESC') {
-            $return *= -1;
+    // Key-preserving insertion sort; avoids passing any callback to PHP
+    // builtins, which corrupts callable arguments inside a resumed Fiber.
+    $sorted_keys = array_keys($results);
+    $n = count($sorted_keys);
+    for ($i = 1; $i < $n; $i++) {
+      $key_i = $sorted_keys[$i];
+      $j = $i - 1;
+      while ($j >= 0) {
+        $key_j = $sorted_keys[$j];
+        $cmp = 0;
+        foreach ($active_sort_processors as $sort_processor) {
+          if ($cmp = $sort_processor->sortResults($results[$key_i], $results[$key_j])) {
+            if ($sort_processor->getConfiguration()['sort'] == 'DESC') {
+              $cmp *= -1;
+            }
+            break;
           }
+        }
+        if ($cmp < 0) {
+          $sorted_keys[$j + 1] = $sorted_keys[$j];
+          $j--;
+        }
+        else {
           break;
         }
       }
-      return $return;
-    });
+      $sorted_keys[$j + 1] = $key_i;
+    }
+    $sorted = [];
+    foreach ($sorted_keys as $key) {
+      $sorted[$key] = $results[$key];
+    }

     // Loop over the results and see if they have any children, if they do, fire
     // a request to this same method again with the children.
-    foreach ($results as &$result) {
+    foreach ($sorted as $key => $result) {
       if (!empty($result->getChildren())) {
-        $children = $this->sortFacetResults($active_sort_processors, $result->getChildren());
-        $result->setChildren($children);
+        $sorted[$key]->setChildren($this->sortFacetResults($active_sort_processors, $result->getChildren()));
       }
     }

-    return $results;
+    return $sorted;
   }

 }