diff --git a/cluster/aws/util.sh b/cluster/aws/util.sh
index 0b726f55682..065fef7a4bb 100644
--- a/cluster/aws/util.sh
+++ b/cluster/aws/util.sh
@@ -87,7 +87,7 @@ function detect-minions () {
     echo "Found ${MINION_NAMES[$i]} at ${minion_ip}"
     KUBE_MINION_IP_ADDRESSES+=("${minion_ip}")
   done
-  if [ -z "$KUBE_MINION_IP_ADDRESSES" ]; then
+  if [[ -z "$KUBE_MINION_IP_ADDRESSES" ]]; then
     echo "Could not detect Kubernetes minion nodes.  Make sure you've launched a cluster with 'kube-up.sh'"
     exit 1
   fi
@@ -156,7 +156,7 @@ function detect-image () {
 
 # Verify prereqs
 function verify-prereqs {
-  if [ "$(which aws)" == "" ]; then
+  if [[ "$(which aws)" == "" ]]; then
     echo "Can't find aws in PATH, please fix and retry."
     exit 1
   fi
@@ -341,7 +341,7 @@ function kube-up {
   local htpasswd
   htpasswd=$(cat "${KUBE_TEMP}/htpasswd")
 
-  if [ ! -f $AWS_SSH_KEY ]; then
+  if [[ ! -f $AWS_SSH_KEY ]]; then
     ssh-keygen -f $AWS_SSH_KEY -N ''
   fi
 
@@ -351,7 +351,7 @@ function kube-up {
 
   VPC_ID=$($AWS_CMD describe-vpcs | get_vpc_id)
 
-  if [ -z "$VPC_ID" ]; then
+  if [[ -z "$VPC_ID" ]]; then
 	  echo "Creating vpc."
 	  VPC_ID=$($AWS_CMD create-vpc --cidr-block 172.20.0.0/16 | json_val '["Vpc"]["VpcId"]')
 	  $AWS_CMD modify-vpc-attribute --vpc-id $VPC_ID --enable-dns-support '{"Value": true}' > $LOG
@@ -362,7 +362,7 @@ function kube-up {
   echo "Using VPC $VPC_ID"
 
   SUBNET_ID=$($AWS_CMD describe-subnets | get_subnet_id $VPC_ID)
-  if [ -z "$SUBNET_ID" ]; then
+  if [[ -z "$SUBNET_ID" ]]; then
 	  echo "Creating subnet."
 	  SUBNET_ID=$($AWS_CMD create-subnet --cidr-block 172.20.0.0/24 --vpc-id $VPC_ID | json_val '["Subnet"]["SubnetId"]')
   fi
@@ -370,7 +370,7 @@ function kube-up {
   echo "Using subnet $SUBNET_ID"
 
   IGW_ID=$($AWS_CMD describe-internet-gateways | get_igw_id $VPC_ID)
-  if [ -z "$IGW_ID" ]; then
+  if [[ -z "$IGW_ID" ]]; then
 	  echo "Creating Internet Gateway."
 	  IGW_ID=$($AWS_CMD create-internet-gateway | json_val '["InternetGateway"]["InternetGatewayId"]')
 	  $AWS_CMD attach-internet-gateway --internet-gateway-id $IGW_ID --vpc-id $VPC_ID > $LOG
@@ -390,7 +390,7 @@ function kube-up {
 
   SEC_GROUP_ID=$($AWS_CMD describe-security-groups | get_sec_group_id)
 
-  if [ -z "$SEC_GROUP_ID" ]; then
+  if [[ -z "$SEC_GROUP_ID" ]]; then
 	  echo "Creating security group."
 	  SEC_GROUP_ID=$($AWS_CMD create-security-group --group-name kubernetes-sec-group --description kubernetes-sec-group --vpc-id $VPC_ID | json_val '["GroupId"]')
 	  $AWS_CMD authorize-security-group-ingress --group-id $SEC_GROUP_ID --protocol -1 --port all --cidr 0.0.0.0/0 > $LOG
@@ -805,7 +805,7 @@ function ssh-to-node {
   local cmd="$2"
 
   local ip=$(get_instance_public_ip ${node})
-  if [ -z "ip" ]; then
+  if [[ -z "ip" ]]; then
     echo "Could not detect IP for ${node}."
     exit 1
   fi