diff --git a/lib/libsys/intro.2 b/lib/libsys/intro.2
index 4f8a9e221e1..f10312c1962 100644
--- a/lib/libsys/intro.2
+++ b/lib/libsys/intro.2
@@ -37,6 +37,7 @@
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
+.In sys/syscall.h
 .In errno.h
 .Sh DESCRIPTION
 This section contains the system calls which comprise the