diff --git a/scheduler/pthread.c b/scheduler/pthread.c
index ffa6947..e29b7b3 100644
--- a/scheduler/pthread.c
+++ b/scheduler/pthread.c
@@ -29,7 +29,9 @@
 #include <assert.h>
 #include <errno.h>
 #include <stdlib.h>
-#include <unistd.h>
+#ifdef HAVE_UNISTD_H
+# include <unistd.h>
+#endif
 #include <string.h>
 
 #include "winbase.h"