diff --git a/index.js b/index.js
index 3fc0c1a..2e33dc5 100644
--- a/index.js
+++ b/index.js
@@ -13,11 +13,19 @@ var defaults = {
   // just to account for clock skew really
 , _dropDead: 5 * MIN
 };
+var promisify = require('util').promisify;
+if (!promisify) {
+  try {
+    promisify = require('bluebird').promisify;
+  } catch(e) {
+    console.error("You're running an older version of node that doesn't have 'promisify'. Please run 'npm install bluebird --save'.");
+  }
+}
 
 // autoSni = { renewWithin, renewBy, getCertificates, tlsOptions, _dbg_now }
 module.exports.create = function (autoSni) {
 
-  if (!autoSni.getCertificatesAsync) { autoSni.getCertificatesAsync = require('bluebird').promisify(autoSni.getCertificates); }
+  if (!autoSni.getCertificatesAsync) { autoSni.getCertificatesAsync = promisify(autoSni.getCertificates); }
   if (!autoSni.renewWithin) { autoSni.renewWithin = autoSni.notBefore || defaults.renewWithin; }
   if (autoSni.renewWithin < defaults._renewWithinMin) {
     throw new Error("options.renewWithin should be at least " + (defaults._renewWithinMin / DAY) + " days");
@@ -123,7 +131,7 @@ module.exports.create = function (autoSni) {
       else if (certMeta.then) {
         //log(autoSni.debug, "PROMISED CERT", domain);
         // we are already getting a cert
-        promise = certMeta
+        promise = certMeta;
       }
       else if (now >= certMeta.expiresNear) {
         //log(autoSni.debug, "EXPIRED CERT");
diff --git a/package.json b/package.json
index 4ae50da..26c38cc 100644
--- a/package.json
+++ b/package.json
@@ -1,10 +1,10 @@
 {
   "name": "le-sni-auto",
-  "version": "2.1.6",
+  "version": "2.1.8",
   "description": "An auto-sni strategy for registering and renewing letsencrypt certificates using SNICallback",
   "homepage": "https://git.coolaj86.com/coolaj86/le-sni-auto.js",
   "main": "index.js",
-  "dependencies": {
+  "trulyOptionalDependencies": {
     "bluebird": "^3.5.1"
   },
   "devDependencies": {},
@@ -13,7 +13,7 @@
   },
   "repository": {
     "type": "git",
-    "url": "git+https://git.coolaj86.com/coolaj86/le-sni-auto.js.git"
+    "url": "https://git.coolaj86.com/coolaj86/le-sni-auto.js.git"
   },
   "keywords": [
     "le-sni",