diff --git a/cluster/gce/util.sh b/cluster/gce/util.sh
index 54de81ee9bb..121298cb84a 100755
--- a/cluster/gce/util.sh
+++ b/cluster/gce/util.sh
@@ -550,6 +550,8 @@ function create-certs {
     exit 2
   }
   CERT_DIR="${KUBE_TEMP}/easy-rsa-master/easyrsa3"
+  # By default, linux wraps base64 output every 76 cols, so we use 'tr -d' to remove whitespaces.
+  # Note 'base64 -w0' doesn't work on Mac OS X, which has different flags.
   CA_CERT_BASE64=$(cat "${CERT_DIR}/pki/ca.crt" | base64 | tr -d '\r\n')
   MASTER_CERT_BASE64=$(cat "${CERT_DIR}/pki/issued/${MASTER_NAME}.crt" | base64 | tr -d '\r\n')
   MASTER_KEY_BASE64=$(cat "${CERT_DIR}/pki/private/${MASTER_NAME}.key" | base64 | tr -d '\r\n')