diff --git a/packages/codemirror/src/editor.ts b/packages/codemirror/src/editor.ts
index d64dbb47cdd1..b6a0716e04e2 100644
--- a/packages/codemirror/src/editor.ts
+++ b/packages/codemirror/src/editor.ts
@@ -1479,7 +1479,7 @@ namespace Private {
         el.style.fontFamily = value;
         break;
       case 'fontSize':
-        el.style.setProperty('fontSize', value ? value + 'px' : null);
+        el.style.setProperty('font-size', value ? value + 'px' : null);
         break;
       case 'lineHeight':
         el.style.lineHeight = value ? value.toString() : null;