diff --git a/ChangeLog b/ChangeLog
index 2df7099..9ffb81d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,8 +2,9 @@ Easy-RSA 3 ChangeLog
 
 3.1.0 (TBD)
    * Introduce basic support for OpenSSL version 3 (#492)
+   * Update regex in grep to be POSIX compliant (#556)
 
-3.0.9 (2022-05-04)
+3.0.9 (2022-05-xx)
    * Upgrade OpenSSL from 1.1.0j to 1.1.1o (#405, #407) 
       - We are buliding this ourselves now.
    * Fix --version so it uses EASYRSA_OPENSSL (#416)
diff --git a/easyrsa3/easyrsa b/easyrsa3/easyrsa
index 5310bee..8fe9332 100755
--- a/easyrsa3/easyrsa
+++ b/easyrsa3/easyrsa
@@ -2370,7 +2370,7 @@ default_server_san() {
 		awk -F'=' '/^  *CN=/{print $2}'
 		)"
 
-	if echo "$cn" | grep -E -q '^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$'; then
+	if echo "$cn" | grep -E -q '^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$'; then
 		print "subjectAltName = IP:$cn"
 	else
 		print "subjectAltName = DNS:$cn"