diff --git a/utils/fonts_utils.js b/utils/fonts_utils.js
index ff5e686b5..550637fff 100644
--- a/utils/fonts_utils.js
+++ b/utils/fonts_utils.js
@@ -55,7 +55,7 @@ function readCharset(aStream, aCharstrings) {
  */
 function readCharstringEncoding(aString) {
   if (!aString)
-    return "";
+    return '';
 
   var charstringTokens = [];