diff --git a/newlib/libc/sys/rtems/include/sys/lock.h b/newlib/libc/sys/rtems/include/sys/lock.h
index d6169025b..87cf06fc0 100644
--- a/newlib/libc/sys/rtems/include/sys/lock.h
+++ b/newlib/libc/sys/rtems/include/sys/lock.h
@@ -27,6 +27,7 @@
 #define _SYS_LOCK_H_
 
 #include <sys/cdefs.h>
+#include <sys/_timespec.h>
 #include <stddef.h>
 
 __BEGIN_DECLS
@@ -298,6 +299,9 @@ void _Semaphore_Wait(struct _Semaphore_Control *);
 int _Semaphore_Wait_timed(struct _Semaphore_Control *,
     const struct timespec *);
 
+int _Semaphore_Wait_timed_clock(struct _Semaphore_Control *,
+    const struct timespec *, __clockid_t);
+
 int _Semaphore_Wait_timed_ticks(struct _Semaphore_Control *, __uint32_t);
 
 int _Semaphore_Try_wait(struct _Semaphore_Control *);