diff --git a/ChangeLog b/ChangeLog
index a6663d4..6833a7c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2018-07-13  Ben Elliston  <bje@gnu.org>
+
+	* config.guess (set_cc_for_build): Disable SC2039 ("In POSIX sh,
+	RANDOM is undefined").
+	* Makefile (shellcheck): Don't disable SC2039 globally.
+
 2018-07-13  Ben Elliston  <bje@gnu.org>
 
 	* config.guess: Disable SC2154 and SC2172 Shellcheck warnings.
diff --git a/Makefile b/Makefile
index 9744deb..edab683 100644
--- a/Makefile
+++ b/Makefile
@@ -17,4 +17,4 @@ check-sub:
 	cd testsuite && sh config-sub.sh
 
 shellcheck:
-	shellcheck -e SC2006,SC2039 -f gcc config.guess config.sub testsuite/*.sh
+	shellcheck -e SC2006 -f gcc config.guess config.sub testsuite/*.sh
diff --git a/config.guess b/config.guess
index ab55d4d..ced991e 100755
--- a/config.guess
+++ b/config.guess
@@ -101,6 +101,7 @@ trap 'exitcode=$?; test -z "$tmp" || rm -fr "$tmp"; exit $exitcode' 0
 
 set_cc_for_build() {
     : "${TMPDIR=/tmp}"
+    # shellcheck disable=SC2039
     { tmp=`(umask 077 && mktemp -d "$TMPDIR/cgXXXXXX") 2>/dev/null` && test -n "$tmp" && test -d "$tmp" ; } ||
 	{ test -n "$RANDOM" && tmp=$TMPDIR/cg$$-$RANDOM && (umask 077 && mkdir "$tmp" 2>/dev/null) ; } ||
 	{ tmp=$TMPDIR/cg-$$ && (umask 077 && mkdir "$tmp" 2>/dev/null) && echo "Warning: creating insecure temp directory" >&2 ; } ||