diff --git a/lib/acme-client.js b/lib/acme-client.js
index 5dd199f..1bb3794 100644
--- a/lib/acme-client.js
+++ b/lib/acme-client.js
@@ -11,9 +11,14 @@ module.exports.create = function (deps) {
   var NOOP=function () {};
   var log=NOOP;
   var request=require('request');
-  var generateSignature=deps.RSA.signJws;
+  var RSA = deps.RSA;
+  var generateSignature = RSA.signJws;
 
   function Acme(keypair) {
+    if ('string' === typeof keypair) {
+      // backwards compat
+      keypair = RSA.import({ privateKeyPem: keypair });
+    }
     this.keypair = keypair;
     this.nonces=[];
   }