diff --git a/lib/platform.browser.js b/lib/platform.browser.js
index 0429522..86d9148 100644
--- a/lib/platform.browser.js
+++ b/lib/platform.browser.js
@@ -68,19 +68,17 @@ exports.pow = function(opts) {
   var poolSize = opts.poolSize || navigator.hardwareConcurrency;
   poolSize = poolSize || FAILBACK_POOL_SIZE;
 
-  // Check all input params prematurely to not let promise executor or
-  // worker to fail because of it.
-  assert(typeof poolSize === "number", "Bad pool size");
-  assert(poolSize >= 1, "Pool size is too low");
-  assert(poolSize <= 1024, "Pool size is too high");
-  assert(typeof opts.target === "number", "Bad target");
-  assert(opts.target >= 0, "Target is too low");
-  assert(opts.target <= 9007199254740991, "Target is too high");
-  assert(Buffer.isBuffer(opts.initialHash), "Bad initial hash");
-  assert(opts.initialHash.length === 64, "Bad initial hash");
-
   var cancel;
   var promise = new Promise(function(resolve, reject) {
+    assert(typeof poolSize === "number", "Bad pool size");
+    assert(poolSize >= 1, "Pool size is too low");
+    assert(poolSize <= 1024, "Pool size is too high");
+    assert(typeof opts.target === "number", "Bad target");
+    assert(opts.target >= 0, "Target is too low");
+    assert(opts.target <= 9007199254740991, "Target is too high");
+    assert(Buffer.isBuffer(opts.initialHash), "Bad initial hash");
+    assert(opts.initialHash.length === 64, "Bad initial hash");
+
     function terminateAll() {
       while (workers.length) {
         workers.shift().terminate();
diff --git a/lib/platform.js b/lib/platform.js
index c8b47f8..8a5529e 100644
--- a/lib/platform.js
+++ b/lib/platform.js
@@ -53,18 +53,6 @@ exports.getTarget = function(opts) {
 
 exports.pow = function(opts) {
   var poolSize = opts.poolSize || os.cpus().length;
-
-  // Check all input params prematurely to not let promise executor or
-  // worker to fail because of it.
-  assert(typeof poolSize === "number", "Bad pool size");
-  assert(poolSize >= 1, "Pool size is too low");
-  assert(poolSize <= 1024, "Pool size is too high");
-  assert(typeof opts.target === "number", "Bad target");
-  assert(opts.target >= 0, "Target is too low");
-  assert(opts.target <= 9007199254740991, "Target is too high");
-  assert(Buffer.isBuffer(opts.initialHash), "Bad initial hash");
-  assert(opts.initialHash.length === 64, "Bad initial hash");
-
   // TODO(Kagami): Allow to cancel a POW (see `platform.browser.js`).
   return new promise(function(resolve, reject) {
     worker.powAsync(
diff --git a/src/worker.cc b/src/worker.cc
index 7d8c63f..d159f92 100644
--- a/src/worker.cc
+++ b/src/worker.cc
@@ -78,11 +78,15 @@ NAN_METHOD(PowAsync) {
   size_t pool_size = args[0]->Uint32Value();
   uint64_t target = args[1]->IntegerValue();
   size_t length = Buffer::Length(args[2]->ToObject());
-  if (pool_size < 1 || pool_size > MAX_POOL_SIZE || length != HASH_SIZE) {
+  char* buf = Buffer::Data(args[2]->ToObject());
+  if (
+      pool_size < 1 ||
+      pool_size > MAX_POOL_SIZE ||
+      length != HASH_SIZE ||
+      buf == NULL) {
     return NanThrowError("Bad input");
   }
 
-  char* buf = Buffer::Data(args[2]->ToObject());
   // TODO(Kagami): Do we need to process `std::bad_alloc`?
   uint8_t* initial_hash = new uint8_t[length];
   memcpy(initial_hash, buf, length);
diff --git a/test.js b/test.js
index b49d1b7..dbc2d61 100644
--- a/test.js
+++ b/test.js
@@ -312,10 +312,15 @@ describe("POW", function() {
     expect(POW.check({nonce: 3122436, target: 4864647698763, initialHash: Buffer("8ff2d685db89a0af2e3dbfd3f700ae96ef4d9a1eac72fd778bbb368c7510cddda349e03207e1c4965bd95c6f7265e8f1a481a08afab3874eaafb9ade09a10880", "hex")})).to.be.false;
   });
 
-  it("should fail on bad POW arguments", function() {
-    expect(POW.doAsync.bind(null, {target: 123, initialHash: 0})).to.throw(Error);
-    expect(POW.doAsync.bind(null, {target: 123, initialHash: Buffer("test")})).to.throw(Error);
-    expect(POW.doAsync.bind(null, {poolSize: -1, target: 123, initialHash: Buffer(64)})).to.throw(Error);
+  it("should reject promise on bad POW arguments", function(done) {
+    POW.doAsync({target: 123, initialHash: {}}).catch(function() {
+      POW.doAsync({target: 123, initialHash: Buffer("test")}).catch(function() {
+        POW.doAsync({poolSize: -1, target: 123, initialHash: Buffer(64)})
+        .catch(function() {
+          done();
+        });
+      });
+    });
   });
 
   if (allTests) {