diff --git a/src/acme2.js b/src/acme2.js
index b60ccedfc..ef4ff8c02 100644
--- a/src/acme2.js
+++ b/src/acme2.js
@@ -294,7 +294,7 @@ Acme2.prototype.signCertificate = async function (finalizationUrl, csrPem) {
     assert.strictEqual(typeof finalizationUrl, 'string');
     assert.strictEqual(typeof csrPem, 'string');
 
-    const csrDer = await shell.spawn('openssl', ['req', '-inform', 'pem', '-outform', 'der'], { input: csrPem, encoding: 'buffer' });
+    const csrDer = await shell.spawn('openssl', ['req', '-inform', 'pem', '-outform', 'der'], { input: csrPem });
 
     const payload = {
         csr: b64(csrDer)