diff --git a/lib/ecdsa.js b/lib/ecdsa.js
index 14eee00..b22c409 100644
--- a/lib/ecdsa.js
+++ b/lib/ecdsa.js
@@ -156,6 +156,9 @@ ECDSA.prototype.sign = function() {
   if (!hashbuf || !privkey || !d)
     throw new Error('invalid parameters');
 
+  if (!Buffer.isBuffer(hashbuf) || hashbuf.length !== 32)
+    throw new Error('hashbuf must be a 32 byte buffer');
+
   var N = Point.getN();
   var G = Point.getG();
   var e = BN().fromBuffer(hashbuf);
diff --git a/test/ecdsa.js b/test/ecdsa.js
index c285a4d..0291e21 100644
--- a/test/ecdsa.js
+++ b/test/ecdsa.js
@@ -144,6 +144,17 @@ describe("ECDSA", function() {
       ecdsa.verify().should.equal(true);
     });
 
+    it('should should throw an error if hashbuf is not 32 bytes', function() {
+      var ecdsa2 = ECDSA().set({
+        hashbuf: ecdsa.hashbuf.slice(0, 31),
+        keypair: ecdsa.keypair
+      });
+      ecdsa2.randomK();
+      (function() {
+        ecdsa2.sign();
+      }).should.throw('hashbuf must be a 32 byte buffer');
+    });
+
   });
 
   describe('#signRandomK', function() {