diff --git a/simpleheat.js b/simpleheat.js
index dc06eb9..23760ec 100644
--- a/simpleheat.js
+++ b/simpleheat.js
@@ -48,7 +48,8 @@ simpleheat.prototype = {
     },
 
     radius: function (r, blur) {
-        blur = blur === undefined ? 15 : blur;
+        r = parseFloat(r);
+        blur = blur === undefined ? 15 : parseFloat(blur);
 
         // create a grayscale blurred circle image that we'll use for drawing points
         var circle = this._circle = this._createCanvas(),