diff --git a/src/BookSearch/BookSearch.php b/src/BookSearch/BookSearch.php
index a683419..51e4d6e 100644
--- a/src/BookSearch/BookSearch.php
+++ b/src/BookSearch/BookSearch.php
@@ -180,7 +180,7 @@ class BookSearch
         if(isset($results['response']['docs']) && is_array($results['response']['docs'])) {
             foreach($results['response']['docs'] as $r) {
                 if (!isset($r['id'])) continue;
-                $books[] = $r;
+                $books[$r['id']] = $r;
             }
         }