diff --git a/bin/tests/system/dnssec/tests.sh b/bin/tests/system/dnssec/tests.sh
index 5fa3a5ce2e..7e479b29dc 100644
--- a/bin/tests/system/dnssec/tests.sh
+++ b/bin/tests/system/dnssec/tests.sh
@@ -2770,10 +2770,10 @@ $DIG $ANSWEROPTS expiring.example soa @10.53.0.4 > dig.out.ns4.2.$n
 ttls=`awk '$1 != ";;" {print $2}' dig.out.ns4.1.$n`
 ttls2=`awk '$1 != ";;" {print $2}' dig.out.ns4.2.$n`
 for ttl in ${ttls:-0}; do
-    [ ${ttl:-0} -eq 300 ] || ret=1
+    [ "${ttl}" -eq 300 ] || ret=1
 done
 for ttl in ${ttls2:-0}; do
-    [ ${ttl:-0} -le 60 ] || ret=1
+    [ "${ttl}" -le 60 ] || ret=1
 done
 n=`expr $n + 1`
 if [ $ret != 0 ]; then echo_i "failed"; fi
@@ -2791,7 +2791,7 @@ for ttl in ${ttls:-300}; do
     [ "$ttl" -le 300 ] && [ "$ttl" -gt 240 ] || ret=1
 done
 for ttl in ${ttls2:-0}; do
-    [ ${ttl:-0} -le 60 ] || ret=1
+    [ "$ttl" -le 60 ] || ret=1
 done
 n=`expr $n + 1`
 if [ $ret != 0 ]; then echo_i "failed"; fi
@@ -2809,7 +2809,7 @@ for ttl in ${ttls:-300}; do
     [ "$ttl" -le 300 ] && [ "$ttl" -gt 240 ] || ret=1
 done
 for ttl in ${ttls2:-0}; do
-    [ ${ttl:-0} -le 60 ] || ret=1
+    [ "$ttl" -le 60 ] || ret=1
 done
 n=`expr $n + 1`
 if [ $ret != 0 ]; then echo_i "failed"; fi