diff --git a/lib/node-progress.js b/lib/node-progress.js
index 8eb0740..400be28 100644
--- a/lib/node-progress.js
+++ b/lib/node-progress.js
@@ -53,6 +53,9 @@ function ProgressBar(fmt, options) {
     options = options || {};
     if ('string' != typeof fmt) throw new Error('format required');
     if ('number' != typeof options.total) throw new Error('total required');
+    if (options.curr % 1 !== 0 || options.curr < 0 || options.curr >= options.total) {
+      throw new Error('current required nature number and is less than or equal to total');
+    }
   }
 
   this.fmt = fmt;
@@ -70,6 +73,10 @@ function ProgressBar(fmt, options) {
   this.callback = options.callback || function () {};
   this.tokens = {};
   this.lastDraw = '';
+  // start time for eta
+  if (this.curr >= 0 && this.curr <= this.total) {
+    this.start = new Date;
+  } 
 }
 
 /**
@@ -88,9 +95,6 @@ ProgressBar.prototype.tick = function(len, tokens){
   if ('object' == typeof len) tokens = len, len = 1;
   if (tokens) this.tokens = tokens;
 
-  // start time for eta
-  if (0 == this.curr) this.start = new Date;
-
   this.curr += len
 
   // try to render