diff --git a/man2/mprotect.2 b/man2/mprotect.2
index ae305f6..5ba6c58 100644
--- a/man2/mprotect.2
+++ b/man2/mprotect.2
@@ -38,16 +38,19 @@
 .\"
 .TH MPROTECT 2 2015-07-23 "Linux" "Linux Programmer's Manual"
 .SH NAME
-mprotect \- set protection on a region of memory
+mprotect, mprotect_key \- set protection on a region of memory
 .SH SYNOPSIS
 .nf
 .B #include <sys/mman.h>
 .sp
 .BI "int mprotect(void *" addr ", size_t " len ", int " prot );
+.BI "int mprotect_key(void *" addr ", size_t " len ", int " prot , " unsigned long " key);
 .fi
 .SH DESCRIPTION
 .BR mprotect ()
-changes protection for the calling process's memory page(s)
+and
+.BR mprotect_key ()
+change protection for the calling process's memory page(s)
 containing any part of the address range in the
 interval [\fIaddr\fP,\ \fIaddr\fP+\fIlen\fP\-1].
 .I addr
@@ -74,10 +77,18 @@ The memory can be modified.
 .TP
 .B PROT_EXEC
 The memory can be executed.
+.PP
+.I key
+is the protection or storage key to assign to the memory.
+The number of keys supported is dependent on the architecture
+and is always at least one.
+The default key is 0.
 .SH RETURN VALUE
 On success,
 .BR mprotect ()
-returns zero.
+and
+.BR mprotect_key ()
+return zero.
 On error, \-1 is returned, and
 .I errno
 is set appropriately.