diff --git a/wagtail/wagtailadmin/static_src/wagtailadmin/scss/components/_icons.scss b/wagtail/wagtailadmin/static_src/wagtailadmin/scss/components/_icons.scss
index e9774fb087..f548b671fe 100644
--- a/wagtail/wagtailadmin/static_src/wagtailadmin/scss/components/_icons.scss
+++ b/wagtail/wagtailadmin/static_src/wagtailadmin/scss/components/_icons.scss
@@ -43,7 +43,7 @@
 
 @each $icon, $content in $icons-after {
     .icon-#{$icon}:after {
-        content: #{$content};
+        content: quote(#{$content});
     }
 }
 
diff --git a/wagtail/wagtailadmin/static_src/wagtailadmin/scss/userbar.scss b/wagtail/wagtailadmin/static_src/wagtailadmin/scss/userbar.scss
index 33cd64e4f4..6ed3108d6f 100644
--- a/wagtail/wagtailadmin/static_src/wagtailadmin/scss/userbar.scss
+++ b/wagtail/wagtailadmin/static_src/wagtailadmin/scss/userbar.scss
@@ -73,7 +73,7 @@ $positions: (
 
 @each $icon, $content in $icons-after {
     .#{$namespace}-icon-#{$icon}:after {
-        content: #{$content};
+        content: quote(#{$content});
     }
 }