diff --git a/README.md b/README.md
index d1ced5f..1165d3f 100644
--- a/README.md
+++ b/README.md
@@ -62,7 +62,7 @@ HANDLE epoll_create1(int flags);
 * Create a new epoll instance (port).
 * `size` is ignored but most be greater than zero.
 * `flags` must be zero as there are no supported flags.
-* Returns `INVALID_HANDLE_VALUE` on failure.
+* Returns `NULL` on failure.
 * [man page][man epoll_create]
 
 ### epoll_close
diff --git a/src/api.c b/src/api.c
index 5fefcc5..7f16269 100644
--- a/src/api.c
+++ b/src/api.c
@@ -35,8 +35,9 @@ static HANDLE _epoll_create(void) {
   if (reflock_tree_add(&_epoll_handle_tree,
                        &port_info->handle_tree_node,
                        (uintptr_t) ephnd) < 0) {
+    /* This should never happen. */
     ep_port_delete(port_info);
-    return_error(INVALID_HANDLE_VALUE, ERROR_ALREADY_EXISTS);
+    return_error(NULL, ERROR_ALREADY_EXISTS);
   }
 
   return ephnd;
@@ -44,14 +45,14 @@ static HANDLE _epoll_create(void) {
 
 HANDLE epoll_create(int size) {
   if (size <= 0)
-    return_error(INVALID_HANDLE_VALUE, ERROR_INVALID_PARAMETER);
+    return_error(NULL, ERROR_INVALID_PARAMETER);
 
   return _epoll_create();
 }
 
 HANDLE epoll_create1(int flags) {
   if (flags != 0)
-    return_error(INVALID_HANDLE_VALUE, ERROR_INVALID_PARAMETER);
+    return_error(NULL, ERROR_INVALID_PARAMETER);
 
   return _epoll_create();
 }
diff --git a/test/test-auto-drop-on-close.c b/test/test-auto-drop-on-close.c
index 7b3cbb2..df2a782 100644
--- a/test/test-auto-drop-on-close.c
+++ b/test/test-auto-drop-on-close.c
@@ -60,7 +60,7 @@ int main(void) {
   int r;
 
   ephnd = epoll_create1(0);
-  check(ephnd != INVALID_HANDLE_VALUE);
+  check(ephnd != NULL);
 
   sock1 = create_and_add_socket(ephnd, EPOLLIN);
   sock2 = create_and_add_socket(ephnd, EPOLLIN);
diff --git a/test/test-multi-poll.c b/test/test-multi-poll.c
index cd68472..643b982 100644
--- a/test/test-multi-poll.c
+++ b/test/test-multi-poll.c
@@ -107,7 +107,7 @@ int main(void) {
 
     /* Create epoll port. */
     port = epoll_create1(0);
-    check(port != INVALID_HANDLE_VALUE);
+    check(port != NULL);
     ports[i] = port;
 
     /* Register recv_sock with the epoll port. */
diff --git a/test/test-oneshot-and-hangup.c b/test/test-oneshot-and-hangup.c
index 725c080..ecf58c9 100644
--- a/test/test-oneshot-and-hangup.c
+++ b/test/test-oneshot-and-hangup.c
@@ -65,7 +65,7 @@ int main(void) {
   {
     /* Create an epoll instance. */
     epoll_port = epoll_create(1);
-    check(epoll_port > 0);
+    check(epoll_port != NULL);
   }
 
   {
diff --git a/test/test-udp-pings.c b/test/test-udp-pings.c
index 428ed15..704e375 100644
--- a/test/test-udp-pings.c
+++ b/test/test-udp-pings.c
@@ -24,7 +24,7 @@ int main(void) {
   struct epoll_event ev;
 
   epoll_hnd = epoll_create1(0);
-  check(epoll_hnd && epoll_hnd != INVALID_HANDLE_VALUE);
+  check(epoll_hnd != NULL);
 
   srv = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
   r = ioctlsocket(srv, FIONBIO, &one);