diff --git a/src/browser/ui/dom/CSSProperty.js b/src/browser/ui/dom/CSSProperty.js
index cc051ec7a0..50f0802300 100644
--- a/src/browser/ui/dom/CSSProperty.js
+++ b/src/browser/ui/dom/CSSProperty.js
@@ -15,6 +15,8 @@
  * CSS properties which accept numbers but are not in units of "px".
  */
 var isUnitlessNumber = {
+  boxFlex: true,
+  boxFlexGroup: true,
   columnCount: true,
   flex: true,
   flexGrow: true,