diff --git a/bin/letsencrypt-add.sh b/bin/letsencrypt-add.sh
index dd66f71..85056da 100755
--- a/bin/letsencrypt-add.sh
+++ b/bin/letsencrypt-add.sh
@@ -32,7 +32,7 @@ while getopts "hd:" opt; do
     d ) # domain name (hostname) to create cert for
       domain=${OPTARG,,}
       # basic but good enough domain name regex validation
-      if [[ ! $domain =~ ^(([a-zA-Z](-?[a-zA-Z0-9])*)\.)+[a-zA-Z]{2,}$ ]] ; then
+      if [[ ! $domain =~ ^(([a-zA-Z0-9](-?[a-zA-Z0-9])*)\.)+[a-zA-Z]{2,}$ ]] ; then
         echo "ERROR: Invalid domain name: $1"
         exit 1
       fi
diff --git a/bin/letsencrypt-certonly.sh b/bin/letsencrypt-certonly.sh
index dffc9cf..168cae6 100755
--- a/bin/letsencrypt-certonly.sh
+++ b/bin/letsencrypt-certonly.sh
@@ -34,7 +34,7 @@ while getopts "hd:tn" opt; do
     d ) # domain name (hostname) to create cert for
       domain=${OPTARG,,}
       # basic but good enough domain name regex validation
-      if [[ ! $domain =~ ^(([a-zA-Z](-?[a-zA-Z0-9])*)\.)+[a-zA-Z]{2,}$ ]] ; then
+      if [[ ! $domain =~ ^(([a-zA-Z0-9](-?[a-zA-Z0-9])*)\.)+[a-zA-Z]{2,}$ ]] ; then
         echo "ERROR: Invalid domain name: $1"
         exit 1
       fi