diff --git a/man2/sigaction.2 b/man2/sigaction.2
index 564c3a057..6cd795459 100644
--- a/man2/sigaction.2
+++ b/man2/sigaction.2
@@ -733,10 +733,10 @@ allowed the receipt of any signal, not just the one we are installing
 settings).
 .PP
 .BR sigaction ()
-can be called with a null second argument to query the current signal
+can be called with a NULL second argument to query the current signal
 handler.
 It can also be used to check whether a given signal is valid for
-the current machine by calling it with null second and third arguments.
+the current machine by calling it with NULL second and third arguments.
 .PP
 It is not possible to block
 .BR SIGKILL " or " SIGSTOP