diff --git a/lib/cmd.js b/lib/cmd.js
index b0452cc..0235b38 100644
--- a/lib/cmd.js
+++ b/lib/cmd.js
@@ -39,6 +39,11 @@ module.exports = {
     if (!pid){
       throw new Error('PID is required for the kill operation.');
     }
+
+    if (typeof isNaN(pid)) {
+      throw new Error('PID must be a number.')
+    }
+
     callback = callback || function(){};
     if (typeof force == 'function'){
       callback = force;
diff --git a/package.json b/package.json
index 050c778..8683b44 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "node-windows",
-  "version": "1.0.0-beta.5",
+  "version": "1.0.0-beta.6",
   "description": "Support for Windows services, event logging, UAC, and several helper methods for interacting with the OS.",
   "keywords": [
     "ngn",