diff --git a/mode/cobol/index.html b/mode/cobol/index.html
index 326e398b678580f0b8bfb438efb63047748e00a3..a6c5c339ca0ff19288186b1d6158cfd8839ade94 100644
--- a/mode/cobol/index.html
+++ b/mode/cobol/index.html
@@ -193,7 +193,7 @@
       function selectFontsize() {
         var fontSizeInput = document.getElementById("selectFontSize");
         var fontSize = fontSizeInput.options[fontSizeInput.selectedIndex].innerHTML;
-        editor.getWrapperElement().style["font-size"] = fontSize;
+        editor.getWrapperElement().style.fontSize = fontSize;
         editor.refresh();
       }
       function selectReadOnly() {