diff --git a/js/jquery.knob.js b/js/jquery.knob.js
index a2fb82a..ff555ab 100755
--- a/js/jquery.knob.js
+++ b/js/jquery.knob.js
@@ -153,6 +153,8 @@
                 this.v = this.$.val();
                 (this.v === '') && (this.v = this.o.min);
 
+                this.v = this.v.replace(/[^0-9.\-]/g, '');
+
                 this.$.bind(
                     'change blur'
                     , function () {
@@ -763,4 +765,4 @@
         ).parent();
     };
 
-})(jQuery);
\ No newline at end of file
+})(jQuery);