diff --git a/man2/sigprocmask.2 b/man2/sigprocmask.2
index 24c06c944..197ea7580 100644
--- a/man2/sigprocmask.2
+++ b/man2/sigprocmask.2
@@ -86,6 +86,11 @@ but the current value of the signal mask is nevertheless returned in
 .I oldset
 (if it is not NULL).
 
+A set of functions for modifying and inspecting variables of type
+.I sigset_t
+("signal sets") is described in
+.BR sigsetops (3).
+
 The use of
 .BR sigprocmask ()
 is unspecified in a multithreaded process; see