diff --git a/uloop.h b/uloop.h
index bce3974..05007fa 100644
--- a/uloop.h
+++ b/uloop.h
@@ -21,6 +21,7 @@
 #define _ULOOP_H__
 
 #include <sys/time.h>
+#include <sys/types.h>
 #include <stdbool.h>
 #include <stdint.h>
 #include <signal.h>