diff --git a/lib/private/Share20/DefaultShareProvider.php b/lib/private/Share20/DefaultShareProvider.php
index 3fd09ed676f2..3a5bfd22c713 100644
--- a/lib/private/Share20/DefaultShareProvider.php
+++ b/lib/private/Share20/DefaultShareProvider.php
@@ -948,7 +948,7 @@ private function resolveGroupShares($shares, $userId) {
 
 				// Ensure uniquenes of parents
 				if (!isset($shareParents[$shareParent])) {
-					$shareParents[] = $shareParent;
+					$shareParents[$shareParent] = true;
 				} else {
 					throw new ProviderException('Parent of share should be unique');
 				}