diff --git a/lib/private/Files/Cache/CacheEntry.php b/lib/private/Files/Cache/CacheEntry.php
index 8ac76acf6d140..3c93296ff62d5 100644
--- a/lib/private/Files/Cache/CacheEntry.php
+++ b/lib/private/Files/Cache/CacheEntry.php
@@ -137,7 +137,7 @@ public function getUnencryptedSize(): int {
 		if (isset($this->data['unencrypted_size']) && $this->data['unencrypted_size'] > 0) {
 			return $this->data['unencrypted_size'];
 		} else {
-			return $this->data['size'];
+			return $this->data['size'] ?? 0;
 		}
 	}
 }