diff --git a/man2/mprotect.2 b/man2/mprotect.2
index 604682203..fbf6d2244 100644
--- a/man2/mprotect.2
+++ b/man2/mprotect.2
@@ -87,7 +87,12 @@ The memory cannot be accessed.
 \fIaddr\fR is not a valid pointer, or not a multiple of PAGESIZE.
 .TP
 .B ENOMEM
-Internal kernel structures could not be allocated.
+Internal kernel structures could not be allocated.  
+Or: addreses  in the range
+.RI [ addr ,
+.IR addr + len ]
+are invalid for the address space of the process,
+or specify one or more pages that are not mapped.
 .SH EXAMPLE
 .nf
 #include <stdio.h>