diff --git a/phpseclib/Crypt/EC/BaseCurves/Montgomery.php b/phpseclib/Crypt/EC/BaseCurves/Montgomery.php
index c6fb7441c..9909d621a 100644
--- a/phpseclib/Crypt/EC/BaseCurves/Montgomery.php
+++ b/phpseclib/Crypt/EC/BaseCurves/Montgomery.php
@@ -221,7 +221,7 @@ private function doubleAndAddPoint(array $p, array $q, PrimeInteger $x1): array
     public function multiplyPoint(array $p, BigInteger $d): array
     {
         $p1 = [$this->one, $this->zero];
-        $alreadyInternal = isset($x[1]);
+        $alreadyInternal = isset($p[1]);
         $p2 = $this->convertToInternal($p);
         $x = $p[0];