diff --git a/lib/platform.js b/lib/platform.js
index 3a7fc3d..c8b47f8 100644
--- a/lib/platform.js
+++ b/lib/platform.js
@@ -56,14 +56,14 @@ exports.pow = function(opts) {
 
   // Check all input params prematurely to not let promise executor or
   // worker to fail because of it.
-  // 1 - UINT32_MAX
-  assert(poolSize > 0, "Pool size is too low");
-  assert(poolSize <= 4294967295, "Pool size is too high");
-  // 0 - (2^53 - 1)
+  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) {
diff --git a/src/pow.cc b/src/pow.cc
index aa78c15..9da2f8e 100644
--- a/src/pow.cc
+++ b/src/pow.cc
@@ -9,15 +9,15 @@
 #include <pthread.h>
 #include <arpa/inet.h>
 #include <openssl/sha.h>
+#include "./pow.h"
 
-#define HASH_SIZE 64
-
-typedef enum {
-  RESULT_NOT_READY,
-  RESULT_OK,
-  RESULT_OVERFLOW,
-  RESULT_ERROR
-} Result;
+enum PowResult {
+  RESULT_OK = 0,
+  RESULT_OVERFLOW = -1,
+  RESULT_ERROR = -2,
+  RESULT_BAD_INPUT = -3,
+  RESULT_NOT_READY = -4
+};
 
 // Global arguments.
 size_t g_pool_size;
@@ -27,7 +27,7 @@ uint64_t g_max_nonce;
 
 // Shared variables for threads.
 pthread_mutex_t g_mutex;
-Result g_result = RESULT_NOT_READY;
+PowResult g_result = RESULT_NOT_READY;
 uint64_t g_nonce;
 
 inline uint64_t ntohll(uint64_t x) {
@@ -38,7 +38,7 @@ inline uint64_t ntohll(uint64_t x) {
 }
 
 // Set POW computation result in a thread-safe way.
-void set_result(Result res, uint64_t nonce) {
+void set_result(PowResult res, uint64_t nonce) {
   pthread_mutex_lock(&g_mutex);
   if (g_result == RESULT_NOT_READY) {
     g_result = res;
@@ -87,6 +87,9 @@ int pow(size_t pool_size,
         const uint8_t* initial_hash,
         uint64_t max_nonce,
         uint64_t* nonce) {
+  if (pool_size < 1 || pool_size > MAX_POOL_SIZE) {
+    return RESULT_BAD_INPUT;
+  }
   g_pool_size = pool_size;
   g_target = target;
   g_initial_hash = (uint8_t *)initial_hash;
@@ -112,18 +115,10 @@ int pow(size_t pool_size,
     pthread_join(threads[i], NULL);
   }
 
-  switch (g_result) {
-    case RESULT_OK:
-      *nonce = g_nonce;
-      error = 0;
-      break;
-    case RESULT_OVERFLOW:
-      error = -1;
-      break;
-    default:
-      error = -2;
+  if (g_result == RESULT_OK) {
+    *nonce = g_nonce;
   }
 
   pthread_mutex_destroy(&g_mutex);
-  return error;
+  return g_result;
 }
diff --git a/src/pow.h b/src/pow.h
index e4cce93..28bc894 100644
--- a/src/pow.h
+++ b/src/pow.h
@@ -1,6 +1,9 @@
 #ifndef BITMESSAGE_POW_H
 #define BITMESSAGE_POW_H
 
+#define MAX_POOL_SIZE 1024
+#define HASH_SIZE 64
+
 int pow(size_t pool_size,
         uint64_t target,
         const uint8_t* initial_hash,
diff --git a/src/worker.cc b/src/worker.cc
index 3116a2d..c265505 100644
--- a/src/worker.cc
+++ b/src/worker.cc
@@ -68,22 +68,32 @@ class PowWorker : public NanAsyncWorker {
 NAN_METHOD(PowAsync) {
   NanScope();
 
-  NanCallback *callback = new NanCallback(args[3].As<Function>());
+  if (args.Length() != 4 ||
+      !args[0]->IsNumber() ||  // pool_size
+      !args[1]->IsNumber() ||  // target
+      !args[2]->IsObject() ||  // initial_hash
+      !args[3]->IsFunction()) {  // cb
+    NanThrowError("Bad input");
+    NanReturnUndefined();
+  }
+
   size_t pool_size = args[0]->Uint32Value();
   uint64_t target = args[1]->IntegerValue();
   size_t length = Buffer::Length(args[2]->ToObject());
-  char* buf = Buffer::Data(args[2]->ToObject());
+  if (pool_size < 1 || pool_size > MAX_POOL_SIZE || length != HASH_SIZE) {
+    NanThrowError("Bad input");
+    NanReturnUndefined();
+  }
   uint8_t* initial_hash = (uint8_t *)malloc(length);
-
   if (initial_hash == NULL) {
-    Local<Value> argv[] = {NanError("Internal error")};
-    callback->Call(1, argv);
-  } else {
-    memcpy(initial_hash, buf, length);
-    NanAsyncQueueWorker(
-        new PowWorker(callback, pool_size, target, initial_hash));
+    NanThrowError("Internal error");
+    NanReturnUndefined();
   }
 
+  char* buf = Buffer::Data(args[2]->ToObject());
+  memcpy(initial_hash, buf, length);
+  NanCallback* callback = new NanCallback(args[3].As<Function>());
+  NanAsyncQueueWorker(new PowWorker(callback, pool_size, target, initial_hash));
   NanReturnUndefined();
 }