diff --git a/doc/man/s3fs.1 b/doc/man/s3fs.1
index 6061a05..fe629c6 100644
--- a/doc/man/s3fs.1
+++ b/doc/man/s3fs.1
@@ -226,6 +226,11 @@ If allow_other option is not set, s3fs allows access to the mount point only to
 In the opposite case s3fs allows access to all users as the default.
 But if you set the allow_other with this option, you can control the permissions of the mount point by this option like umask.
 .TP
+\fB\-o\fR umask (default is "0000")
+sets umask for files under the mountpoint.  This can allow
+users other than the mounting user to read and write to files
+that they did not create.
+.TP
 \fB\-o\fR nomultipart - disable multipart uploads
 .TP
 \fB\-o\fR enable_content_md5 (default is disable)
diff --git a/src/s3fs_util.cpp b/src/s3fs_util.cpp
index c99e208..0e370b4 100644
--- a/src/s3fs_util.cpp
+++ b/src/s3fs_util.cpp
@@ -1290,6 +1290,11 @@ void show_help ()
     "      this option, you can control the permissions of the\n"
     "      mount point by this option like umask.\n"
     "\n"
+    "   umask (default is \"0000\")\n"
+    "      - sets umask for files under the mountpoint.  This can allow\n"
+	"      users other than the mounting user to read and write to files\n"
+	"      that they did not create.\n"
+    "\n"
     "   nomultipart (disable multipart uploads)\n"
     "\n"
     "   enable_content_md5 (default is disable)\n"