diff --git a/sys/sys/priority.h b/sys/sys/priority.h
--- a/sys/sys/priority.h
+++ b/sys/sys/priority.h
@@ -34,6 +34,8 @@
 #ifndef _SYS_PRIORITY_H_
 #define _SYS_PRIORITY_H_
 
+#include <sys/types.h>
+
 /*
  * Process priority specifications.
  */
diff --git a/sys/sys/rtprio.h b/sys/sys/rtprio.h
--- a/sys/sys/rtprio.h
+++ b/sys/sys/rtprio.h
@@ -34,6 +34,7 @@
 #ifndef _SYS_RTPRIO_H_
 #define _SYS_RTPRIO_H_
 
+#include <sys/types.h>
 #include <sys/priority.h>
 
 /*