diff --git a/js/usercss.js b/js/usercss.js
index 45a7c762..1cfdd142 100644
--- a/js/usercss.js
+++ b/js/usercss.js
@@ -238,7 +238,7 @@ var usercss = (() => {
           result.default = range[0];
           result.min = range[1];
           result.max = range[2];
-          result.step = range[3];
+          result.step = range[3] || 1;
         }
         break;
       }