diff --git a/lib/aws.js b/lib/aws.js
index 0ad6aba..7d3c609 100644
--- a/lib/aws.js
+++ b/lib/aws.js
@@ -33,17 +33,17 @@ function checkCredentials(obj, cb) {
   if (obj.secretAccessKey == null || obj.accessKeyId == null || lapse > 0) {
     var md = metadata.init();
     md().call({endpoint: 'iam/security-credentials/'}, function(err, res) {
-      if (err) cb(err);
-      if (typeof res === 'undefined') cb(new Error('metadata API response undefined'));
+      if (err) return cb(err);
+      if (typeof res === 'undefined') return cb(new Error('metadata API response undefined'));
       md().call({endpoint: 'iam/security-credentials/' + res.split('\n')[0]},
        function(err, res) {
         try {
           res = JSON.parse(res);
         } catch(e) {
-          cb(e);
+          return cb(e);
         }
         if (res.SecretAccessKey === null)
-          cb(new Error("secretAccessKey and accessKeyId not provided and could not be determined."));
+          return cb(new Error("secretAccessKey and accessKeyId not provided and could not be determined."));
         obj.secretAccessKey = res.SecretAccessKey;
         obj.accessKeyId = res.AccessKeyId;
         obj.token = res.Token;