diff --git a/README.md b/README.md
index 33feec6..47aecb4 100644
--- a/README.md
+++ b/README.md
@@ -38,6 +38,11 @@ cronExp.build();
 // '* * * * *'
 ```
 
+The cron values are stored with the following keys, which must match identically when getting and setting:
+```JavaScript
+'minute', 'hour', 'dayOfTheMonth', 'month', 'dayOfTheWeek'
+```
+
 API includes basic getters and setters:
 ```JavaScript
 cronExp.get('minute');
diff --git a/cron-builder.js b/cron-builder.js
index 6cd20fd..c5f8b99 100644
--- a/cron-builder.js
+++ b/cron-builder.js
@@ -41,7 +41,7 @@ var CronValidator = (function() {
 
         for (var measureOfTime in expression) {
             if (expression.hasOwnProperty(measureOfTime)) {
-                this.validateValue(measureOfTime, expression[measureOfTime]);
+                this.validateValue(measureOfTime, expression[measureOfTime][0]);
             }
         }
     },
@@ -89,6 +89,14 @@ var CronValidator = (function() {
             throw new Error('Invalid value; Only numbers 0-9, "-", and "*" chars are allowed');
         }
 
+        if (!measureOfTime || !value) {
+            throw new Error('Missing arguments; Both measureOfTime and value are required arguments');
+        }
+
+        if (typeof(value) !== 'string') {
+            throw new Error('value argument must be a string');
+        }
+
         if (value !== '*') {
             // check to see if value is within range if value is not '*'
             if (value.indexOf('-') >= 0) {
@@ -102,7 +110,6 @@ var CronValidator = (function() {
                     throw new Error('Invalid value; top of range is not valid for "' + measureOfTime + '". Limit is ' + validatorObj[measureOfTime].max + '.');
                 }
             } else {
-
                 if (parseInt(value) < validatorObj[measureOfTime].min) {
                     throw new Error('Invalid value; given value is not valid for "' + measureOfTime + '". Minimum value is "' + validatorObj[measureOfTime].min + '".');
                 }
@@ -113,7 +120,6 @@ var CronValidator = (function() {
         }
     };
 
-
     return {
         measureOfTimeValues: MeasureOfTimeValues,
         validateExpression: validateExpression,