diff --git a/lib/libsys/munmap.2 b/lib/libsys/munmap.2
--- a/lib/libsys/munmap.2
+++ b/lib/libsys/munmap.2
@@ -25,7 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd January 15, 2025
+.Dd January 16, 2025
 .Dt MUNMAP 2
 .Os
 .Sh NAME
@@ -66,6 +66,15 @@
 .Xr mprotect 2 ,
 .Xr msync 2 ,
 .Xr getpagesize 3
+.Sh STANDARDS
+The
+.Fn munmap
+system call conforms to
+.St -p1003.1-2024 .
+Portable programs should ensure that
+.Fa addr
+is a multiple of the page size as returned by
+.Xr sysconf 3 .
 .Sh HISTORY
 The
 .Fn munmap