Index: lib/libc/gen/sigsetops.3
===================================================================
--- lib/libc/gen/sigsetops.3	(revision 215310)
+++ lib/libc/gen/sigsetops.3	(working copy)
@@ -92,8 +92,11 @@
 The
 .Fn sigismember
 function returns 1
-if the signal is a member of the set,
-0 otherwise.
+if the signal is a member of the set, or 0 if it is not.
+Otherwise, it returns \-1 and the global variable
+.Va errno
+is set to indicate the reason.
+.Bl
 The other functions return 0 upon success.
 A \-1 return value
 indicates an error occurred and the global variable