diff --git a/less/mixins.less b/less/mixins.less
index cb3b12968c..727cf55a11 100644
--- a/less/mixins.less
+++ b/less/mixins.less
@@ -376,14 +376,15 @@
 
 // Retina images
 //
-// Short retina mixin for setting background-image and -size
+// Short retina mixin for setting background-image and -size. Note that the
+// spelling of `min--moz-device-pixel-ratio` is intentional.
 
 .img-retina(@file-1x; @file-2x; @width-1x; @height-1x) {
   background-image: url("@{file-1x}");
 
   @media
   only screen and (-webkit-min-device-pixel-ratio: 2),
-  only screen and (   min--moz-device-pixel-ratio: 2), // Not a typo
+  only screen and (   min--moz-device-pixel-ratio: 2),
   only screen and (     -o-min-device-pixel-ratio: 2/1),
   only screen and (        min-device-pixel-ratio: 2),
   only screen and (                min-resolution: 192dpi),