diff --git a/lib/cipherModes.js b/lib/cipherModes.js
index 339915cc..1583e96b 100644
--- a/lib/cipherModes.js
+++ b/lib/cipherModes.js
@@ -731,6 +731,8 @@ modes.gcm.prototype.decrypt = function(input, output, finish) {
   }
 };
 
+var unauthenticException = new Error('Error: MAC Mispatch. Content and/or MAC has been tempared with');
+
 modes.gcm.prototype.afterFinish = function(output, options) {
   var rval = true;
 
@@ -760,7 +762,7 @@ modes.gcm.prototype.afterFinish = function(output, options) {
 
   // check authentication tag
   if(options.decrypt && this.tag.bytes() !== this._tag) {
-    rval = false;
+    throw unauthenticException;
   }
 
   return rval;