diff --git a/src/ClaimingOrganisation.php b/src/ClaimingOrganisation.php
index 6ad6454..6508d76 100644
--- a/src/ClaimingOrganisation.php
+++ b/src/ClaimingOrganisation.php
@@ -6,7 +6,7 @@ class ClaimingOrganisation
 {
     private $name = '';
     private $hmrcRef = '';
-    private ?string $regulator;
+    private ?string $regulator = null;
     private $regNo = '';
     private $hasConnectedCharities = false;
     private $connectedCharities = [];
@@ -51,7 +51,7 @@ public function setHmrcRef($value)
         $this->hmrcRef = $value;
     }
 
-    public function getRegulator()
+    public function getRegulator(): ?string
     {
         return $this->regulator;
     }
diff --git a/src/GiftAid.php b/src/GiftAid.php
index 256f313..dd55329 100644
--- a/src/GiftAid.php
+++ b/src/GiftAid.php
@@ -1036,7 +1036,11 @@ protected function writeClaimStartData(XMLWriter $package, ClaimingOrganisation
         } else {
             $package->writeElement('OtherReg', $org->getRegulator());
         }
-        $package->writeElement('RegNo', $org->getRegNo());
+
+        if ($org->getRegulator() !== null && !empty($org->getRegNo())) {
+            $package->writeElement('RegNo', $org->getRegNo());
+        }
+
         $package->endElement(); # Regulator
 
         $package->startElement('Repayment');