diff --git a/npm-shrinkwrap.json b/npm-shrinkwrap.json
index b972861bc..28f96dfa8 100644
--- a/npm-shrinkwrap.json
+++ b/npm-shrinkwrap.json
@@ -2746,20 +2746,27 @@
       "from": "underscore@>=1.7.0 <2.0.0",
       "resolved": "https://registry.npmjs.org/underscore/-/underscore-1.8.3.tgz"
     },
-    "ursa": {
-      "version": "0.9.4",
-      "from": "ursa@>=0.9.3 <0.10.0",
-      "resolved": "https://registry.npmjs.org/ursa/-/ursa-0.9.4.tgz",
+    "ursa-purejs": {
+      "version": "0.0.3",
+      "from": "ursa-purejs@*",
+      "resolved": "https://registry.npmjs.org/ursa-purejs/-/ursa-purejs-0.0.3.tgz",
       "dependencies": {
-        "bindings": {
-          "version": "1.2.1",
-          "from": "bindings@>=1.2.1 <2.0.0",
-          "resolved": "https://registry.npmjs.org/bindings/-/bindings-1.2.1.tgz"
-        },
-        "nan": {
-          "version": "2.4.0",
-          "from": "nan@>=2.3.3 <3.0.0",
-          "resolved": "https://registry.npmjs.org/nan/-/nan-2.4.0.tgz"
+        "node-rsa": {
+          "version": "0.2.30",
+          "from": "node-rsa@>=0.2.23 <0.3.0",
+          "resolved": "https://registry.npmjs.org/node-rsa/-/node-rsa-0.2.30.tgz",
+          "dependencies": {
+            "asn1": {
+              "version": "0.2.3",
+              "from": "asn1@0.2.3",
+              "resolved": "https://registry.npmjs.org/asn1/-/asn1-0.2.3.tgz"
+            },
+            "lodash": {
+              "version": "3.3.0",
+              "from": "lodash@3.3.0",
+              "resolved": "https://registry.npmjs.org/lodash/-/lodash-3.3.0.tgz"
+            }
+          }
         }
       }
     },
diff --git a/package.json b/package.json
index c2020c0f9..d0521d5a9 100644
--- a/package.json
+++ b/package.json
@@ -64,7 +64,7 @@
     "tail-stream": "https://registry.npmjs.org/tail-stream/-/tail-stream-0.2.1.tgz",
     "tldjs": "^1.6.2",
     "underscore": "^1.7.0",
-    "ursa": "^0.9.3",
+    "ursa-purejs": "0.0.3",
     "valid-url": "^1.0.9",
     "validator": "^4.9.0",
     "x509": "^0.2.4"
diff --git a/src/cert/acme.js b/src/cert/acme.js
index 0afce8976..f7df4b142 100644
--- a/src/cert/acme.js
+++ b/src/cert/acme.js
@@ -10,7 +10,7 @@ var assert = require('assert'),
     paths = require('../paths.js'),
     safe = require('safetydance'),
     superagent = require('superagent'),
-    ursa = require('ursa'),
+    ursa = require('ursa-purejs'),
     util = require('util'),
     _ = require('underscore');
 
@@ -97,7 +97,7 @@ Acme.prototype.sendSignedRequest = function (url, payload, callback) {
             n: b64(privateKey.getModulus())
         }
     };
- 
+
     var payload64 = b64(payload);
 
     this.getNonce(function (error, nonce) {
@@ -345,7 +345,7 @@ Acme.prototype.downloadChain = function (linkHeader, callback) {
     if (!linkHeader) return new AcmeError(AcmeError.EXTERNAL_ERROR, 'Empty link header when downloading certificate chain');
 
     var linkInfo = parseLinks(linkHeader);
-    if (!linkInfo || !linkInfo.up) return new AcmeError(AcmeError.EXTERNAL_ERROR, 'Failed to parse link header when downloading certificate chain'); 
+    if (!linkInfo || !linkInfo.up) return new AcmeError(AcmeError.EXTERNAL_ERROR, 'Failed to parse link header when downloading certificate chain');
 
     debug('downloadChain: downloading from %s', this.caOrigin + linkInfo.up);