diff --git a/phpseclib/Math/PrimeField/Integer.php b/phpseclib/Math/PrimeField/Integer.php
index c24f4e18..7edfd6c6 100644
--- a/phpseclib/Math/PrimeField/Integer.php
+++ b/phpseclib/Math/PrimeField/Integer.php
@@ -294,8 +294,11 @@ class Integer extends Base
      */
     public function toBytes(): string
     {
-        $length = static::$modulo[$this->instanceID]->getLengthInBytes();
-        return str_pad($this->value->toBytes(), $length, "\0", STR_PAD_LEFT);
+        if (isset(static::$modulo[$this->instanceID])) {
+            $length = static::$modulo[$this->instanceID]->getLengthInBytes();
+            return str_pad($this->value->toBytes(), $length, "\0", STR_PAD_LEFT);
+        }
+        return $this->value->toBytes();
     }
 
     /**
diff --git a/tests/Unit/Math/PrimeFieldTest.php b/tests/Unit/Math/PrimeFieldTest.php
index 0567fdbd..470ce815 100644
--- a/tests/Unit/Math/PrimeFieldTest.php
+++ b/tests/Unit/Math/PrimeFieldTest.php
@@ -22,4 +22,21 @@ class PrimeFieldTest extends PhpseclibTestCase
 
         echo $num2->squareRoot();
     }
+
+    /**
+     * @group github1929
+     */
+    public function testGarbageCollectedToBytes()
+    {
+        $blob = base64_decode('BFgsTFQeqKr0toyURbtT43INMDS7FTHjz3yn3MR1/Yv/pb2b9ZCYNQ/Tafe5hQpEJ4TpZOKfikP/hWZvFL8QCPgqbIGqw/KTfA==');
+        $public = "\0" . substr($blob, 0, 49);
+        $private = substr($blob, -24);
+
+        $point = \phpseclib3\Crypt\EC\Formats\Keys\PKCS1::extractPoint(
+            $public,
+            new \phpseclib3\Crypt\EC\Curves\secp192r1()
+        );
+
+        $this->assertIsString($point[0]->toBytes());
+    }
 }