diff --git a/src/eckey.js b/src/eckey.js
index c5a35bd..6c73877 100644
--- a/src/eckey.js
+++ b/src/eckey.js
@@ -85,6 +85,10 @@ ECKey.prototype.toHex = function() {
 
 ECKey.prototype.toBytes = function() {
   var bytes = this.priv.toByteArrayUnsigned()
+
+  // ensure 32 bytes
+  while (bytes.length < 32) bytes.unshift(0)
+
   if (this.compressed) bytes.push(1)
   return bytes
 }