diff --git a/scripts/pi-hole/js/groups-clients.js b/scripts/pi-hole/js/groups-clients.js
index 49da0613..c883e5f5 100644
--- a/scripts/pi-hole/js/groups-clients.js
+++ b/scripts/pi-hole/js/groups-clients.js
@@ -257,22 +257,20 @@ function addClient() {
 
   if (ip.length === 0) {
     utils.enableAll();
-    utils.showAlert("warning", "", "Warning", "Please specify a client IP address");
+    utils.showAlert("warning", "", "Warning", "Please specify a client IP or MAC address");
     return;
   }
 
-  // Validate IP address (may contain CIDR details)
-  var ipv6format = ip.includes(":");
+  // Convert input to upper case (important for MAC addresses)
+  ip = ip.toUpperCase();
 
-  if (!ipv6format && !utils.validateIPv4CIDR(ip)) {
+  // Validate input, can be:
+  // - IPv4 address (with and without CIDR)
+  // - IPv6 address (with and without CIDR)
+  // - MAC address (in the form AA:BB:CC:DD:EE:FF)
+  if (!utils.validateIPv4CIDR(ip) && !utils.validateIPv6CIDR(ip) && !utils.validateMAC(ip)) {
     utils.enableAll();
-    utils.showAlert("warning", "", "Warning", "Invalid IPv4 address!");
-    return;
-  }
-
-  if (ipv6format && !utils.validateIPv6CIDR(ip)) {
-    utils.enableAll();
-    utils.showAlert("warning", "", "Warning", "Invalid IPv6 address!");
+    utils.showAlert("warning", "", "Warning", "Input is neither an IP nor a MAC address!");
     return;
   }
 
diff --git a/scripts/pi-hole/js/groups-common.js b/scripts/pi-hole/js/groups-common.js
index b0156b0e..8283b0ad 100644
--- a/scripts/pi-hole/js/groups-common.js
+++ b/scripts/pi-hole/js/groups-common.js
@@ -129,6 +129,11 @@ function validateIPv6CIDR(ip) {
   return ipv6validator.test(ip);
 }
 
+function validateMAC(mac) {
+  var macvalidator = new RegExp(/^([\dA-F]{2}:){5}([\dA-F]{2})$/);
+  return macvalidator.test(mac);
+}
+
 function bsSelect_defaults() {
   // set bootstrap-select defaults
   var pickerDEFAULTS = $.fn.selectpicker.Constructor.DEFAULTS;
@@ -157,6 +162,7 @@ window.utils = (function () {
     enableAll: enableAll,
     validateIPv4CIDR: validateIPv4CIDR,
     validateIPv6CIDR: validateIPv6CIDR,
+    validateMAC: validateMAC,
     bsSelect_defaults: bsSelect_defaults
   };
 })();