diff --git a/lib/minimizer.php b/lib/minimizer.php
index 2650c579c1ddbaa56660aaa6664475f50e4d7e0b..3bf5ff9980b8457dc72a8cebc5f5b5742e4f001a 100644
--- a/lib/minimizer.php
+++ b/lib/minimizer.php
@@ -25,12 +25,15 @@ abstract class OC_Minimizer {
 		$cache = OC_Cache::getGlobalCache();
 		if (!OC_Request::isNoCache() && (!defined('DEBUG') || !DEBUG)){
 			$gzout = $cache->get($cache_key.'.gz');
-			OC_Response::setETagHeader(md5($gzout));
+			if ($gzout) {
+				OC_Response::setETagHeader(md5($gzout));
+			}
 		}
 
 		if (!$gzout) {
 			$out = $this->minimizeFiles($files);
 			$gzout = gzencode($out);
+			OC_Response::setETagHeader(md5($gzout));
 			$cache->set($cache_key.'.gz', $gzout);
 		}
 		if ($encoding = OC_Request::acceptGZip()) {