diff --git a/src/test_certs_r4.sh b/src/test_certs_r4.sh
index cce6277..787b505 100755
--- a/src/test_certs_r4.sh
+++ b/src/test_certs_r4.sh
@@ -6,7 +6,7 @@ if [ $# -lt 1 ]; then
 fi
 
 verifier=$1
-if [ $verifier != "bc" ] && [ $verifier != "oqs"]; then
+if [[ $verifier != "bc" ]] && [[ $verifier != "oqs"]]; then
     echo "ERROR: verifier \"$verifier\" not supported"
     exit -1
 fi
@@ -57,10 +57,10 @@ test_ta () {
     printf "\nTesting %s\n" $tafile >> $logfile
 
     # The actual openssl command that is the heart of this script
-    if [ $verifier == "bc" ]; then
+    if [[ $verifier == "bc" ]]; then
         output=$(verify_r3.sh $(pwd)/$tafile 2>&1)
         status=$?
-    elif [ $verifier == "oqs" ]; then
+    elif [[ $verifier == "oqs" ]]; then
         output=$(openssl verify -check_ss_sig -verbose -CAfile $tafile $tafile 2>&1)
         status=$?
     else