diff --git a/lib/bip32.js b/lib/bip32.js
index 0df8129..9e20626 100644
--- a/lib/bip32.js
+++ b/lib/bip32.js
@@ -8,7 +8,9 @@ var Random = require('./random');
 var bn = require('./bn');
 var constants = require('./constants');
 
-var BIP32 = function(str) {
+var BIP32 = function BIP32(str) {
+  if (!(this instanceof BIP32))
+    return new BIP32(str);
   if (str === 'testnet' || str === 'mainnet') {
     this.version = constants[str].bip32privkey;
     this.fromRandom();
diff --git a/lib/ecdsa.js b/lib/ecdsa.js
index 76cd580..38b0ce9 100644
--- a/lib/ecdsa.js
+++ b/lib/ecdsa.js
@@ -6,7 +6,9 @@ var Privkey = require('./privkey');
 var Pubkey = require('./pubkey');
 var Random = require('./random');
 
-var ECDSA = function(hash, key, sig, k) {
+var ECDSA = function ECDSA(hash, key, sig, k) {
+  if (!(this instanceof ECDSA))
+    return new ECDSA(hash, key, sig, k);
   this.hash = hash;
   this.key = key;
   this.sig = sig;
diff --git a/lib/key.js b/lib/key.js
index cefc341..c48d3f6 100644
--- a/lib/key.js
+++ b/lib/key.js
@@ -5,7 +5,9 @@ var Random = require('./random');
 var Bn = require('./bn');
 var point = require('./point');
 
-function Key(privkey, pubkey) {
+var Key = function Key(privkey, pubkey) {
+  if (!(this instanceof Key))
+    return new Key(privkey, pubkey);
   this.privkey = privkey;
   this.pubkey = pubkey;
 };
diff --git a/lib/privkey.js b/lib/privkey.js
index 7aa09cd..bed0b23 100644
--- a/lib/privkey.js
+++ b/lib/privkey.js
@@ -3,7 +3,9 @@ var point = require('./point');
 var constants = require('./constants');
 var base58check = require('./base58check');
 
-var Privkey = function(bn, network, compressed) {
+var Privkey = function Privkey(bn, network, compressed) {
+  if (!(this instanceof Privkey))
+    return new Privkey(bn, network, compressed);
   this.bn = bn;
   this.network = network;
   this.compressed = compressed;
diff --git a/lib/pubkey.js b/lib/pubkey.js
index ded1060..1199034 100644
--- a/lib/pubkey.js
+++ b/lib/pubkey.js
@@ -1,7 +1,9 @@
 var Point = require('./point');
 var bn = require('./bn');
 
-var Pubkey = function(point) {
+var Pubkey = function Pubkey(point) {
+  if (!(this instanceof Pubkey))
+    return new Pubkey(point);
   if (point && !point.getX() && !point.getY())
     throw new Error('pubkey: Invalid point');
   this.point = point;
diff --git a/lib/signature.js b/lib/signature.js
index 451358e..8d911a1 100644
--- a/lib/signature.js
+++ b/lib/signature.js
@@ -1,6 +1,8 @@
 var bn = require('./bn');
 
-var Signature = function(r, s) {
+var Signature = function Signature(r, s) {
+  if (!(this instanceof Signature))
+    return new Signature(r, s);
   this.r = r;
   this.s = s;
 };