diff --git a/acme.sh b/acme.sh
index 195adee0..78a6ec6a 100755
--- a/acme.sh
+++ b/acme.sh
@@ -548,7 +548,7 @@ _createkey() {
 _is_idn() {
   _is_idn_d="$1"
   _debug2 _is_idn_d "$_is_idn_d"
-  _idn_temp=$(printf "%s" "$_is_idn_d" | tr -d '0-9' | tr -d 'a-z' | tr -d 'A-Z' | tr -d '.,-')
+  _idn_temp=$(printf "%s" "$_is_idn_d" | tr -d '[0-9]' | tr -d '[a-z]' | tr -d '[A-Z]' | tr -d '.,-')
   _debug2 _idn_temp "$_idn_temp"
   [ "$_idn_temp" ]
 }
diff --git a/dnsapi/dns_lexicon.sh b/dnsapi/dns_lexicon.sh
index 4cec7cb7..c3628a0f 100755
--- a/dnsapi/dns_lexicon.sh
+++ b/dnsapi/dns_lexicon.sh
@@ -29,7 +29,7 @@ dns_lexicon_add() {
   _savedomainconf PROVIDER "$PROVIDER"
   export PROVIDER
 
-  Lx_name=$(echo LEXICON_${PROVIDER}_USERNAME | tr 'a-z' 'A-Z')
+  Lx_name=$(echo LEXICON_${PROVIDER}_USERNAME | tr '[a-z]' '[A-Z]')
   eval Lx_name_v="\$$Lx_name"
   _debug "$Lx_name" "$Lx_name_v"
   if [ "$Lx_name_v" ]; then
@@ -37,7 +37,7 @@ dns_lexicon_add() {
     export "$Lx_name"
   fi
 
-  Lx_token=$(echo LEXICON_${PROVIDER}_TOKEN | tr 'a-z' 'A-Z')
+  Lx_token=$(echo LEXICON_${PROVIDER}_TOKEN | tr '[a-z]' '[A-Z]')
   eval Lx_token_v="\$$Lx_token"
   _debug "$Lx_token" "$Lx_token_v"
   if [ "$Lx_token_v" ]; then
@@ -45,7 +45,7 @@ dns_lexicon_add() {
     export "$Lx_token"
   fi
 
-  Lx_password=$(echo LEXICON_${PROVIDER}_PASSWORD | tr 'a-z' 'A-Z')
+  Lx_password=$(echo LEXICON_${PROVIDER}_PASSWORD | tr '[a-z]' '[A-Z]')
   eval Lx_password_v="\$$Lx_password"
   _debug "$Lx_password" "$Lx_password_v"
   if [ "$Lx_password_v" ]; then
@@ -53,7 +53,7 @@ dns_lexicon_add() {
     export "$Lx_password"
   fi
 
-  Lx_domaintoken=$(echo LEXICON_${PROVIDER}_DOMAINTOKEN | tr 'a-z' 'A-Z')
+  Lx_domaintoken=$(echo LEXICON_${PROVIDER}_DOMAINTOKEN | tr '[a-z]' '[A-Z]')
   eval Lx_domaintoken_v="\$$Lx_domaintoken"
   _debug "$Lx_domaintoken" "$Lx_domaintoken_v"
   if [ "$Lx_domaintoken_v" ]; then