diff --git a/scss/mixins/_grid.scss b/scss/mixins/_grid.scss
index e48e3db5db..468bb39f28 100644
--- a/scss/mixins/_grid.scss
+++ b/scss/mixins/_grid.scss
@@ -46,6 +46,9 @@
 @mixin make-col-span($size, $columns: $grid-columns) {
   @if $enable-flex {
     flex: 0 0 percentage($size / $columns);
+    // Add a `max-width` to ensure content within each column does not blow out
+    // the width of the column. Applies to IE10+ and Firefox. Chrome and Safari
+    // do not appear to require this.
     max-width: percentage($size / $columns);
   } @else {
     width: percentage($size / $columns);