diff --git a/src/HAB/Pica/Record/Subfield.php b/src/HAB/Pica/Record/Subfield.php
index 0309aabcaa5a421a5d11e18e43a6d7363751d45a..fa8087fd8729dc960b66fccf962a4a35bba22153 100644
--- a/src/HAB/Pica/Record/Subfield.php
+++ b/src/HAB/Pica/Record/Subfield.php
@@ -38,7 +38,7 @@ class Subfield
      *
      * @var string
      */
-    public static $validSubfieldCodePattern = '/^[a-z0-9]$/Di';
+    public static $validSubfieldCodePattern = '/^[a-z0-9#]$/Di';
 
     /**
      * Return true if argument is a valid subfield code.
@@ -149,4 +149,4 @@ class Subfield
     {
         return $this->getValue();
     }
-}
\ No newline at end of file
+}