diff --git a/morris.coffee b/morris.coffee
index cfa245f..9094096 100644
--- a/morris.coffee
+++ b/morris.coffee
@@ -287,7 +287,7 @@ class window.Morris.Line
       # calculate a decimal-year value
       year + (timestamp - y1) / (y2 - y1);
     else
-      parseInt(d, 10)
+      parseInt(date, 10)
 
   # make long numbers prettier by inserting commas
   # eg: commas(1234567) -> '1,234,567'
diff --git a/morris.js b/morris.js
index ed82be8..19be20f 100644
--- a/morris.js
+++ b/morris.js
@@ -303,7 +303,7 @@
         y2 = new Date(year + 1, 0, 1).getTime();
         return year + (timestamp - y1) / (y2 - y1);
       } else {
-        return parseInt(d, 10);
+        return parseInt(date, 10);
       }
     };