diff --git a/include/linux/errno.h b/include/linux/errno.h
index d90b80f9b28c..46685832ed99 100644
--- a/include/linux/errno.h
+++ b/include/linux/errno.h
@@ -5,7 +5,12 @@
 
 #ifdef __KERNEL__
 
-/* Should never be seen by user programs */
+/*
+ * These should never be seen by user programs.  To return one of ERESTART*
+ * codes, signal_pending() MUST be set.  Note that ptrace can observe these
+ * at syscall exit tracing, but they will never be left for the debugged user
+ * process to see.
+ */
 #define ERESTARTSYS	512
 #define ERESTARTNOINTR	513
 #define ERESTARTNOHAND	514	/* restart if no handler.. */