diff --git a/karma.conf.js b/karma.conf.js
index ac0286f..298b387 100644
--- a/karma.conf.js
+++ b/karma.conf.js
@@ -16,10 +16,7 @@ module.exports = function(config) {
   var customLaunchers = {};
   var browsers = [];
 
-  if (!process.env.SAUCE_USERNAME || !process.env.SAUCE_ACCESS_KEY) {
-    console.log('Running locally since SAUCE_USERNAME and SAUCE_ACCESS_KEY environment variables are set.');
-    browsers = ['Firefox', 'Chrome', 'Safari', 'Opera'];
-  } else {
+  if (process.env.SAUCE_USERNAME || process.env.SAUCE_ACCESS_KEY) {
     customLaunchers = {};
 
     var runAll = true;
@@ -99,6 +96,12 @@ module.exports = function(config) {
     }
 
     browsers = Object.keys(customLaunchers);
+  } else if (process.env.TRAVIS_PULL_REQUEST && process.env.TRAVIS_PULL_REQUEST !== 'false') {
+    console.log('Cannot run on Sauce Labs as encrypted environment variables are not available to PRs. Using PhantomJS.');
+    browsers = ['PhantomJS'];
+  } else {
+    console.log('Running locally since SAUCE_USERNAME and SAUCE_ACCESS_KEY environment variables are not set.');
+    browsers = ['Firefox', 'Chrome', 'Safari', 'Opera'];
   }
 
   config.set({
@@ -199,7 +202,7 @@ module.exports = function(config) {
       }
     },
 
-    
+
     // Coverage reporting
     coverageReporter: {
       type: 'lcov',