diff --git a/include/uniproc.h b/include/uniproc.h
index c08a656..189e4a7 100644
--- a/include/uniproc.h
+++ b/include/uniproc.h
@@ -22,6 +22,5 @@ bool uniproc_are_processes_finished(const uniproc_process* p, const size_t num_p
 void uniproc_nullify_processes(uniproc_process* p, const size_t num_processes);
 bool uniproc_is_process_null(const uniproc_process* p);
 void uniproc_await_any_processes(const uniproc_process* p, const size_t num_processes);
-void uniproc_set_userdata(uniproc_process* p, const uint64_t userdata);
 void uniproc_set_userdata(uniproc_process* p, void const* userdata);
 void* uniproc_get_userdata(uniproc_process* p);
\ No newline at end of file
diff --git a/src/uniproc_unix.c b/src/uniproc_unix.c
index 68471b7..b6cf81e 100644
--- a/src/uniproc_unix.c
+++ b/src/uniproc_unix.c
@@ -142,9 +142,6 @@ void uniproc_await_any_processes(const uniproc_process* p, const size_t num_proc
 		waitpid(0, nullptr, WIFEXITED | WIFSIGNALED | WCOREDUMP);
 }
 
-void uniproc_set_userdata(uniproc_process* p, const uint64_t userdata)
-{ p->userdata = userdata; }
-
 void uniproc_set_userdata(uniproc_process * p, void const* userdata)
 { p->userdata = (uint64_t)userdata; }
 
diff --git a/src/uniproc_win64.c b/src/uniproc_win64.c
index e742145..7ea7292 100644
--- a/src/uniproc_win64.c
+++ b/src/uniproc_win64.c
@@ -150,20 +150,29 @@ uniproc_process uniproc_create_process(const char* cmd, const size_t num_args, c
 
 void uniproc_await_processes(uniproc_process* p, int* return_codes, size_t num_processes)
 {
+	size_t num_valid_handles = 0;
 	HANDLE* h = (HANDLE*)malloc(num_processes*sizeof(HANDLE));
 	for (size_t i = 0; i < num_processes; ++i)
+	{
+		if (uniproc_is_process_null(p + i)) continue;
 		h[i] = (HANDLE)p[i]._proc_hdl;
+		num_valid_handles++;
+	}
 
-	WaitForMultipleObjects(num_processes, h, 1, INFINITE);
+	WaitForMultipleObjects(num_valid_handles, h, 1, INFINITE);
 	free(h);
 
 	if (return_codes == NULL) return;
 	for (size_t i = 0; i < num_processes; ++i)
-		GetExitCodeProcess((HANDLE)p[i]._proc_hdl, (LPDWORD)(return_codes+i));
+	{
+		if (uniproc_is_process_null(p + i)) continue;
+		GetExitCodeProcess((HANDLE)p[i]._proc_hdl, (LPDWORD)(return_codes + i));
+	}
 }
 
 void uniproc_close_process(uniproc_process* p)
 {
+	if (uniproc_is_process_null(p)) return;
 	TerminateProcess((HANDLE)p->_proc_hdl, 2);
 	CloseHandle((HANDLE)p->_proc_hdl);
 	fclose(p->in);
@@ -175,9 +184,16 @@ void uniproc_close_process(uniproc_process* p)
 bool uniproc_are_processes_finished(const uniproc_process* p, const size_t num_processes)
 {
 	HANDLE* h = (HANDLE*)malloc(num_processes*sizeof(HANDLE));
-	DWORD ret = WaitForMultipleObjects(num_processes, h, true, 0);
+	size_t num_valid_handles = 0;
+	for (size_t i = 0; i < num_processes; ++i)
+	{
+		if (uniproc_is_process_null(p + i)) continue;
+		h[i] = (HANDLE)p[i]._proc_hdl;
+		num_valid_handles++;
+	}
+	DWORD ret = WaitForMultipleObjects(num_valid_handles, h, true, 0);
 	free(h);
-	return ret >= WAIT_OBJECT_0 && ret < WAIT_OBJECT_0 + num_processes;
+	return ret >= WAIT_OBJECT_0 && ret < WAIT_OBJECT_0 + num_valid_handles;
 }
 
 void uniproc_nullify_processes(uniproc_process* p, const size_t num_processes)
@@ -189,13 +205,17 @@ void uniproc_is_process_null(const uniproc_process* p)
 void uniproc_await_any_processes(const uniproc_process* p, const size_t num_processes)
 {
 	HANDLE* h = (HANDLE*)malloc(num_processes * sizeof(HANDLE));
-	WaitForMultipleObjects(num_processes, h, false, INFINITE);
+	size_t num_valid_handles = 0;
+	for (size_t i = 0; i < num_processes; ++i)
+	{
+		if (uniproc_is_process_null(p + i)) continue;
+		h[i] = (HANDLE)p[i]._proc_hdl;
+		num_valid_handles++;
+	}
+	WaitForMultipleObjects(num_valid_handles, h, false, INFINITE);
 	free(h);
 }
 
-void uniproc_set_userdata(uniproc_process* p, const uint64_t userdata)
-{ p->userdata = userdata; }
-
 void uniproc_set_userdata(uniproc_process * p, void const* userdata)
 { p->userdata = (uint64_t)userdata; }