diff --git a/BUILDING b/BUILDING
index 993d1e373106..99c0bf38b7a2 100644
--- a/BUILDING
+++ b/BUILDING
@@ -130,6 +130,14 @@ CONFIGURATION
                  configuration file in order to set additional build parame-
                  ters, such as compiler flags.
 
+     BUILDSEED   GCC uses random numbers when compiling C++ code.  This vari-
+                 able seeds the gcc random number generator using the -fran-
+                 dom-seed flag with this value.  By default, it is set to
+                 NetBSD-(majorversion).  Using a fixed value causes C++ bina-
+                 ries to be the same when built from the same sources.  Addi-
+                 tional information is available in the GCC documentation of
+                 -frandom-seed.
+
      DESTDIR     Directory to contain the built NetBSD system.  If set, spe-
                  cial options are passed to the compilation tools to prevent
                  their default use of the host system's /usr/include,
@@ -752,6 +760,9 @@ BUILDING
                (provides a clean starting point).  This will skip deleting
                DESTDIR if building on a native system to the root directory.
 
+     -S seed   Change the value of BUILDSEED to seed.  This should rarely be
+               necessary.
+
      -T tools  Set the value of TOOLDIR to tools.  If a relative path is spec-
                ified, it will be converted to an absolute path before being
                used.  If set, the bootstrap ``make'' will only be rebuilt if
diff --git a/build.sh b/build.sh
index e283b9b228ed..ea369d0bc7d0 100755
--- a/build.sh
+++ b/build.sh
@@ -1,5 +1,5 @@
 #! /usr/bin/env sh
-#	$NetBSD: build.sh,v 1.189 2008/06/27 21:38:36 dyoung Exp $
+#	$NetBSD: build.sh,v 1.190 2008/08/05 19:43:33 perry Exp $
 #
 # Copyright (c) 2001-2005 The NetBSD Foundation, Inc.
 # All rights reserved.
@@ -241,6 +241,10 @@ initdefaults()
 	#
 	DISTRIBVER="$(${HOST_SH} ${TOP}/sys/conf/osrelease.sh)"
 
+	# Set the BUILDSEED to NetBSD-"N"
+	#
+	setmakeenv BUILDSEED "NetBSD-$(${HOST_SH} ${TOP}/sys/conf/osrelease.sh -m)"
+
 	# Set various environment variables to known defaults,
 	# to minimize (cross-)build problems observed "in the field".
 	#
@@ -509,9 +513,10 @@ usage()
 	fi
 	cat <<_usage_
 
-Usage: ${progname} [-EnorUux] [-a arch] [-B buildid] [-C cdextras] [-D dest]
-		[-j njob] [-M obj] [-m mach] [-N noisy] [-O obj] [-R release]
-		[-T tools] [-V var=[value]] [-w wrapper] [-X x11src] [-Z var]
+Usage: ${progname} [-EnorUux] [-a arch] [-B buildid] [-C cdextras]
+		[-D dest] [-j njob] [-M obj] [-m mach] [-N noisy]
+		[-O obj] [-R release] [-S seed] [-T tools]
+		[-V var=[value]] [-w wrapper] [-X x11src] [-Z var]
 		operation [...]
 
  Build operations (all imply "obj" and "tools"):
@@ -562,6 +567,7 @@ Usage: ${progname} [-EnorUux] [-a arch] [-B buildid] [-C cdextras] [-D dest]
     -o          Set MKOBJDIRS=no; do not create objdirs at start of build.
     -R release  Set RELEASEDIR to release.  [Default: releasedir]
     -r          Remove contents of TOOLDIR and DESTDIR before building.
+    -S seed     Set BUILDSEED to seed.  [Default: NetBSD-majorversion]
     -T tools    Set TOOLDIR to tools.  If unset, and TOOLDIR is not set in
                 the environment, ${toolprefix}make will be (re)built unconditionally.
     -U          Set MKUNPRIVED=yes; build without requiring root privileges,
@@ -581,7 +587,7 @@ _usage_
 
 parseoptions()
 {
-	opts='a:B:bC:D:dEhi:j:k:M:m:N:nO:oR:rT:tUuV:w:xX:Z:'
+	opts='a:B:bC:D:dEhi:j:k:M:m:N:nO:oR:rS:T:tUuV:w:xX:Z:'
 	opt_a=no
 
 	if type getopts >/dev/null 2>&1; then
@@ -707,6 +713,11 @@ parseoptions()
 			do_rebuildmake=true
 			;;
 
+		-S)
+			eval ${optargcmd}
+			setmakeenv BUILDSEED "${OPTARG}"
+			;;
+
 		-T)
 			eval ${optargcmd}; resolvepath
 			TOOLDIR="${OPTARG}"
@@ -1141,7 +1152,7 @@ createmakewrapper()
 	eval cat <<EOF ${makewrapout}
 #! ${HOST_SH}
 # Set proper variables to allow easy "make" building of a NetBSD subtree.
-# Generated from:  \$NetBSD: build.sh,v 1.189 2008/06/27 21:38:36 dyoung Exp $
+# Generated from:  \$NetBSD: build.sh,v 1.190 2008/08/05 19:43:33 perry Exp $
 # with these arguments: ${_args}
 #
 
diff --git a/doc/BUILDING.mdoc b/doc/BUILDING.mdoc
index bda376b064cf..0d7f08f83118 100644
--- a/doc/BUILDING.mdoc
+++ b/doc/BUILDING.mdoc
@@ -1,4 +1,4 @@
-.\"	$NetBSD: BUILDING.mdoc,v 1.59 2008/04/30 13:10:49 martin Exp $
+.\"	$NetBSD: BUILDING.mdoc,v 1.60 2008/08/05 19:43:33 perry Exp $
 .\"
 .\" Copyright (c) 2001-2008 The NetBSD Foundation, Inc.
 .\" All rights reserved.
@@ -289,6 +289,16 @@ object directory names, and can be consulted in the
 configuration file in order to set additional build parameters,
 such as compiler flags.
 .
+.It Sy BUILDSEED
+GCC uses random numbers when compiling C++ code.
+This variable seeds the gcc random number generator using
+the -frandom-seed flag with this value.
+By default, it is set to NetBSD-(majorversion).
+Using a fixed value causes C++ binaries to be the same when
+built from the same sources.
+Additional information is available in the GCC
+documentation of -frandom-seed.
+.
 .It Sy DESTDIR
 Directory to contain the built
 .Nx
@@ -1438,6 +1448,13 @@ This will skip deleting
 .Sy DESTDIR
 if building on a native system to the root directory.
 .
+.It Fl S Ar seed
+Change the value of
+.Sy BUILDSEED
+to
+.Ar seed .
+This should rarely be necessary.
+.
 .It Fl T Ar tools
 Set the value of
 .Sy TOOLDIR