diff --git a/snappymail/v/0.0.0/app/libraries/RainLoop/Plugins/Manager.php b/snappymail/v/0.0.0/app/libraries/RainLoop/Plugins/Manager.php
index fffa58ae9..d43b46513 100644
--- a/snappymail/v/0.0.0/app/libraries/RainLoop/Plugins/Manager.php
+++ b/snappymail/v/0.0.0/app/libraries/RainLoop/Plugins/Manager.php
@@ -275,7 +275,7 @@ class Manager
 	public function AddCss(string $sFile, bool $bAdminScope = false) : self
 	{
 		if ($this->bIsEnabled) {
-			$this->aCss[$bAdminScope ? 1 : 0] = $sFile;
+			$this->aCss[$bAdminScope ? 1 : 0][] = $sFile;
 		}
 		return $this;
 	}