diff --git a/bin/tests/system/nsupdate/clean.sh b/bin/tests/system/nsupdate/clean.sh
index aa327f8962..ac3f12f197 100644
--- a/bin/tests/system/nsupdate/clean.sh
+++ b/bin/tests/system/nsupdate/clean.sh
@@ -63,4 +63,5 @@ rm -f perl.update_test.out
 rm -f nsupdate.out*
 rm -f typelist.out.*
 rm -f update.out.*
+rm -f update.in.*
 rm -f verylarge
diff --git a/bin/tests/system/nsupdate/tests.sh b/bin/tests/system/nsupdate/tests.sh
index 88910f95a3..7b9c0e6177 100755
--- a/bin/tests/system/nsupdate/tests.sh
+++ b/bin/tests/system/nsupdate/tests.sh
@@ -750,9 +750,10 @@ ret=0
 echo_i "check that changes to the DNSKEY RRset TTL do not have side effects ($n)"
 $DIG $DIGOPTS +tcp +noadd +nosea +nostat +noquest +nocomm +nocmd dnskey.test. \
         @10.53.0.3 dnskey | \
-	sed -n 's/\(.*\)10.IN/update add \1600 IN/p' |
-	(echo server 10.53.0.3 ${PORT}; cat - ; echo send ) |
-$NSUPDATE
+	awk -v port="${PORT}" 'BEGIN { print "server 10.53.0.3", port; }
+	$2 == 10 && $3 == "IN" && $4 == "DNSKEY" { $2 = 600; print "update add", $0 }
+	END { print "send" }' > update.in.$n
+$NSUPDATE update.in.$n
 
 $DIG $DIGOPTS +tcp +noadd +nosea +nostat +noquest +nocomm +nocmd dnskey.test. \
 	@10.53.0.3 any > dig.out.ns3.$n