diff --git a/src/Modal.vue b/src/Modal.vue
index d463a31..d43d804 100644
--- a/src/Modal.vue
+++ b/src/Modal.vue
@@ -96,7 +96,7 @@
         default: [Number, String],
         validator (value) {
           if (typeof value === 'string') {
-            return this.isPercentage(value)
+            return string.splice(-1) === '%' && !isNaN(parseFloat(string))
           }
 
           if (typeof value === 'number') {
@@ -110,7 +110,7 @@
         validator (value) {
           if (typeof value === 'string') {
             const reg = RegExp('^(\d+|\d+[.]\d+)%?$')
-            return value === 'auto' || this.isPercentage(value)
+            return value === 'auto' || (string.splice(-1) === '%' && !isNaN(parseFloat(string)))
           }
 
           if (typeof value === 'number') {
@@ -278,10 +278,6 @@
         return (typeof modal.height === 'string') ? window.height * parseFloat(modal.height) / 100.0 : modal.height
       },
 
-      isPercentage (string) {
-        return string.splice(-1) === '%' && !isNaN(parseFloat(string))
-      },
-
       resize (event) {
         this.modal.width = event.size.width
         this.modal.height = event.size.height