src/Access/CustomParameterNamesAccessCheck.php |  9 +--------
 src/JsonApiSpec.php                            | 23 ++++++++++++++---------
 2 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/src/Access/CustomParameterNamesAccessCheck.php b/src/Access/CustomParameterNamesAccessCheck.php
index 3632003..46864ee 100644
--- a/src/Access/CustomParameterNamesAccessCheck.php
+++ b/src/Access/CustomParameterNamesAccessCheck.php
@@ -52,14 +52,7 @@ class CustomParameterNamesAccessCheck implements AccessInterface {
     $valid = TRUE;
 
     foreach (array_keys($json_api_params) as $name) {
-      // First, ensure this does not violate "MUST NOT".
-      if (strpbrk($name, JsonApiSpec::MEMBER_NAME_RESERVED_CHARACTERS)) {
-        $valid = FALSE;
-        break;
-      }
-
-      // Second, ensure this complies with "MUST".
-      if (!preg_match(JsonApiSpec::MEMBER_NAME_REGEXP, $name, $m)) {
+      if (!JsonApiSpec::isValidMemberName($name)) {
         $valid = FALSE;
         break;
       }
diff --git a/src/JsonApiSpec.php b/src/JsonApiSpec.php
index f8615c8..6679245 100644
--- a/src/JsonApiSpec.php
+++ b/src/JsonApiSpec.php
@@ -10,15 +10,6 @@ namespace Drupal\jsonapi;
 final class JsonApiSpec {
 
   /**
-   * Member name: reserved characters.
-   *
-   * For use with \strpbrk().
-   *
-   * @see http://jsonapi.org/format/#document-member-names
-   */
-  const MEMBER_NAME_RESERVED_CHARACTERS =  "+,.[]!\"#$%&'()*/:;<=>?@\\^`{}~|\x0\x1\x2\x3\x4\x5\x6\x7\x8\x9\xA\xB\xC\xD\xE\xF\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1A\x1B\x1C\x1D\x1E\x1F\x7F";
-
-  /**
    * Member name: globally allowed characters.
    *
    * U+0080 and above (non-ASCII Unicode characters) are allowed, but are not
@@ -66,4 +57,18 @@ final class JsonApiSpec {
     ')?' .
     '$/u';
 
+  /**
+   * Checks whether the given member name is valid.
+   *
+   * @param string $member_name
+   *   A member name to validate.
+   *
+   * @return bool
+   *
+   * @see http://jsonapi.org/format/#document-member-names
+   */
+  public static function isValidMemberName($member_name) {
+    return preg_match(JsonApiSpec::MEMBER_NAME_REGEXP, $member_name) === 1;
+  }
+
 }