diff --git a/resources/assets/stylesheets/less/schedule.less b/resources/assets/stylesheets/less/schedule.less
index 096ffb6a45faa54a3fdb80fa12cef5c4f1a0950d..5d2e69dc34031aaf8e861fcba47be7fc863c160c 100644
--- a/resources/assets/stylesheets/less/schedule.less
+++ b/resources/assets/stylesheets/less/schedule.less
@@ -266,13 +266,13 @@ td.schedule-adminbind {
             background-color: @calendar-category-15;
         }
         &.schedule-category16 {
-            background-color: $calendar-category-16;
+            background-color: @calendar-category-16;
         }
         &.schedule-category17 {
-            background-color: $calendar-category-17;
+            background-color: @calendar-category-17;
         }
         &.schedule-category18 {
-            background-color: $calendar-category-18;
+            background-color: @calendar-category-18;
         }
         &.schedule-category255 {
             background-color: @calendar-category-255;
@@ -449,36 +449,36 @@ div.schedule_entry {
             }
         }
         &.schedule-category16 {
-            background-color: $calendar-category-16-aux;
-            border: 1px solid $calendar-category-16;
+            background-color: @calendar-category-16-aux;
+            border: 1px solid @calendar-category-16;
             dt {
-                background-color: $calendar-category-16;
-                color: contrast($calendar-category-16, $black, $white);
+                background-color: @calendar-category-16;
+                color: contrast(@calendar-category-16, black, white);
             }
             dd {
-                color: contrast($calendar-category-16-aux, $black, $white);
+                color: contrast(@calendar-category-16-aux, black, white);
             }
         }
         &.schedule-category17 {
-            background-color: $calendar-category-17-aux;
-            border: 1px solid $calendar-category-17;
+            background-color: @calendar-category-17-aux;
+            border: 1px solid @calendar-category-17;
             dt {
-                background-color: $calendar-category-17;
-                color: contrast($calendar-category-17, $black, $white);
+                background-color: @calendar-category-17;
+                color: contrast(@calendar-category-17, black, white);
             }
             dd {
-                color: contrast($calendar-category-17-aux, $black, $white);
+                color: contrast(@calendar-category-17-aux, black, white);
             }
         }
         &.schedule-category18 {
-            background-color: $calendar-category-18-aux;
-            border: 1px solid $calendar-category-18;
+            background-color: @calendar-category-18-aux;
+            border: 1px solid @calendar-category-18;
             dt {
-                background-color: $calendar-category-18;
-                color: contrast($calendar-category-18, $black, $white);
+                background-color: @calendar-category-18;
+                color: contrast(@calendar-category-18, black, white);
             }
             dd {
-                color: contrast($calendar-category-18-aux, $black, $white);
+                color: contrast(@calendar-category-18-aux, black, white);
             }
         }
     }