diff --git a/lib/libc_r/man/pthread_kill.3 b/lib/libc_r/man/pthread_kill.3
index 1b1f0ea0026..2af0c1b8f7a 100644
--- a/lib/libc_r/man/pthread_kill.3
+++ b/lib/libc_r/man/pthread_kill.3
@@ -35,6 +35,7 @@
 .Sh LIBRARY
 .Lb libc_r
 .Sh SYNOPSIS
+.Fd #include <pthread.h>
 .Fd #include <signal.h>
 .Ft int
 .Fn pthread_kill "pthread_t thread" "int sig"
diff --git a/lib/libc_r/man/pthread_sigmask.3 b/lib/libc_r/man/pthread_sigmask.3
index 754c897d6e3..645b3227b61 100644
--- a/lib/libc_r/man/pthread_sigmask.3
+++ b/lib/libc_r/man/pthread_sigmask.3
@@ -35,6 +35,7 @@
 .Sh LIBRARY
 .Lb libc_r
 .Sh SYNOPSIS
+.Fd #include <pthread.h>
 .Fd #include <signal.h>
 .Ft int
 .Fn pthread_sigmask "int how" "const sigset_t *set" "sigset_t *oset"
diff --git a/lib/libpthread/man/pthread_kill.3 b/lib/libpthread/man/pthread_kill.3
index 1b1f0ea0026..2af0c1b8f7a 100644
--- a/lib/libpthread/man/pthread_kill.3
+++ b/lib/libpthread/man/pthread_kill.3
@@ -35,6 +35,7 @@
 .Sh LIBRARY
 .Lb libc_r
 .Sh SYNOPSIS
+.Fd #include <pthread.h>
 .Fd #include <signal.h>
 .Ft int
 .Fn pthread_kill "pthread_t thread" "int sig"
diff --git a/lib/libpthread/man/pthread_sigmask.3 b/lib/libpthread/man/pthread_sigmask.3
index 754c897d6e3..645b3227b61 100644
--- a/lib/libpthread/man/pthread_sigmask.3
+++ b/lib/libpthread/man/pthread_sigmask.3
@@ -35,6 +35,7 @@
 .Sh LIBRARY
 .Lb libc_r
 .Sh SYNOPSIS
+.Fd #include <pthread.h>
 .Fd #include <signal.h>
 .Ft int
 .Fn pthread_sigmask "int how" "const sigset_t *set" "sigset_t *oset"
diff --git a/share/man/man3/pthread_kill.3 b/share/man/man3/pthread_kill.3
index 1b1f0ea0026..2af0c1b8f7a 100644
--- a/share/man/man3/pthread_kill.3
+++ b/share/man/man3/pthread_kill.3
@@ -35,6 +35,7 @@
 .Sh LIBRARY
 .Lb libc_r
 .Sh SYNOPSIS
+.Fd #include <pthread.h>
 .Fd #include <signal.h>
 .Ft int
 .Fn pthread_kill "pthread_t thread" "int sig"
diff --git a/share/man/man3/pthread_sigmask.3 b/share/man/man3/pthread_sigmask.3
index 754c897d6e3..645b3227b61 100644
--- a/share/man/man3/pthread_sigmask.3
+++ b/share/man/man3/pthread_sigmask.3
@@ -35,6 +35,7 @@
 .Sh LIBRARY
 .Lb libc_r
 .Sh SYNOPSIS
+.Fd #include <pthread.h>
 .Fd #include <signal.h>
 .Ft int
 .Fn pthread_sigmask "int how" "const sigset_t *set" "sigset_t *oset"