diff --git a/crt/include/nanoshell/lock.h b/crt/include/nanoshell/lock.h
index 57da06d..cc362a7 100644
--- a/crt/include/nanoshell/lock.h
+++ b/crt/include/nanoshell/lock.h
@@ -6,7 +6,8 @@
 
 #include <nanoshell/lock_types.h>
 
-void LockAcquire (SafeLock *pLock);
-void LockFree (SafeLock *pLock);
+// These APIs are not implemented in user mode:
+// void LockAcquire (SafeLock *pLock);
+// void LockFree (SafeLock *pLock);
 
 #endif//_NANOSHELL_LOCK__H