diff --git a/wagtail/wagtailadmin/static_src/wagtailadmin/scss/components/main-nav.scss b/wagtail/wagtailadmin/static_src/wagtailadmin/scss/components/main-nav.scss
index 38c1ef0c9..b411f2d0b 100644
--- a/wagtail/wagtailadmin/static_src/wagtailadmin/scss/components/main-nav.scss
+++ b/wagtail/wagtailadmin/static_src/wagtailadmin/scss/components/main-nav.scss
@@ -320,7 +320,6 @@ body.explorer-open {
         left:$menu-width;
         overflow:auto;
         max-height:100%;
-        border-right:1px solid rgba(0,0,0,0.1);
 
         h2,ul{
             float:right;