diff --git a/lib/utils/mutate.js b/lib/utils/mutate.js
index 7537542..2a2bf8d 100644
--- a/lib/utils/mutate.js
+++ b/lib/utils/mutate.js
@@ -18,10 +18,14 @@ utils.mutate = {
   },
 
   units: function (str) {
-    let mutator = function (m) {
-      return random.number(4) === 1 ? m : make.unit.unit()
+    let mutator = function (m, p1) {
+      if (random.number(4) === 1) {
+        return m
+      } else {
+        return p1 + make.unit.unit()
+      }
     }
-    return str.replace(/(px|em|ex|ch|rem|mm|cm|in|pt|pc|%')/g, mutator)
+    return str.replace(/(\d*)(px|em|ex|ch|rem|mm|cm|in|pt|pc|%')/g, mutator)
   },
 
   random: function (str) {