diff --git a/lib/utils.js b/lib/utils.js
index 59437da..788bb4c 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -28,7 +28,7 @@ module.exports = class AccessUtils {
 
     // Validate the format of options.groupRoles ($group:[role]).
     this.options.groupRoles.forEach(name => {
-      if (!AccessUtils.isValidPrincipalId(name)) {
+      if (!this.isValidPrincipalId(name)) {
         throw new Error('$name is an invalid access group name.')
       }
     })
@@ -253,7 +253,7 @@ module.exports = class AccessUtils {
    * @param {String} principalId A principalId.
    * @returns {Boolean} Returns true if the principalId is on the expected format.
    */
-  static isValidPrincipalId(principalId) {
+  isValidPrincipalId(principalId) {
     return Boolean(this.extractRoleName(principalId))
   }
 
@@ -263,7 +263,7 @@ module.exports = class AccessUtils {
    * @param {String} principalId A principalId.
    * @returns {Boolean} Returns true if the principalId is on the expected format.
    */
-  static extractRoleName(principalId) {
+  extractRoleName(principalId) {
     return principalId.split(':')[1]
   }
 
@@ -281,7 +281,7 @@ module.exports = class AccessUtils {
       const modelClass = context.model
       const { modelId } = context
       const userId = context.getUserId()
-      const roleName = AccessUtils.extractRoleName(role)
+      const roleName = this.extractRoleName(role)
       const GroupAccess = this.app.models[this.options.groupAccessModel]
       const scope = { }