diff --git a/src/SAML2/Assertion/Processor.php b/src/SAML2/Assertion/Processor.php
index f971e91cc..76a3aa978 100644
--- a/src/SAML2/Assertion/Processor.php
+++ b/src/SAML2/Assertion/Processor.php
@@ -93,7 +93,13 @@ public function decryptAssertions(ArrayCollection $assertions): ArrayCollection
     {
         $decrypted = new ArrayCollection();
         foreach ($assertions->getIterator() as $assertion) {
-            $decrypted->add($this->decryptAssertion($assertion));
+            if ($assertion instanceof EncryptedAssertion) {
+                $decrypted->add($this->decryptAssertion($assertion));
+            } elseif ($assertion instanceof Assertion) {
+                $decrypted->add($assertion);
+            } else {
+                throw new InvalidAssertionException('The assertion must be of type: EncryptedAssertion or Assertion');
+            }
         }
 
         return $decrypted;
diff --git a/tests/SAML2/Assertion/ProcessorTest.php b/tests/SAML2/Assertion/ProcessorTest.php
new file mode 100644
index 000000000..e2eebd849
--- /dev/null
+++ b/tests/SAML2/Assertion/ProcessorTest.php
@@ -0,0 +1,95 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SAML2\Assertion;
+
+use Mockery as m;
+use Mockery\Adapter\Phpunit\MockeryTestCase;
+use Psr\Log\LoggerInterface;
+use SAML2\Assertion\Transformer\TransformerInterface;
+use SAML2\Assertion\Validation\AssertionValidator;
+use SAML2\Assertion\Validation\SubjectConfirmationValidator;
+use SAML2\Configuration\IdentityProvider;
+use SAML2\Signature\Validator;
+use SAML2\Utilities\ArrayCollection;
+use SAML2\XML\saml\Assertion;
+use SAML2\XML\saml\EncryptedAssertion;
+use SAML2\Assertion\Exception\InvalidAssertionException;
+use stdClass;
+
+/**
+ * @runTestsInSeparateProcesses
+ */
+class ProcessorTest extends MockeryTestCase
+{
+    /**
+     * @var Processor
+     */
+    private $processor;
+
+    /**
+     * @var m\MockInterface&Decrypter
+     */
+    private $decrypter;
+
+    protected function setUp(): void
+    {
+        $this->decrypter = m::mock(Decrypter::class);
+        $validator = m::mock(Validator::class);
+        $assertionValidator = m::mock(AssertionValidator::class);
+        $subjectConfirmationValidator = m::mock(SubjectConfirmationValidator::class);
+        $transformer = m::mock(TransformerInterface::class);
+        $identityProvider = new IdentityProvider([]);
+        $logger = m::mock(LoggerInterface::class);
+
+        $this->processor = new Processor(
+            $this->decrypter,
+            $validator,
+            $assertionValidator,
+            $subjectConfirmationValidator,
+            $transformer,
+            $identityProvider,
+            $logger
+        );
+    }
+
+    /**
+     * @test
+     */
+    public function processor_correctly_encrypts_assertions(): void
+    {
+        $encryptedAssertion = \Mockery::mock(EncryptedAssertion::class);
+        $assertion = \Mockery::mock(Assertion::class);
+
+        $testData = [
+            [$assertion],
+            [$encryptedAssertion],
+            [$assertion, $encryptedAssertion, $assertion],
+            [$encryptedAssertion, $encryptedAssertion, $encryptedAssertion],
+        ];
+
+        foreach ($testData as $assertions) {
+            $this->decrypter
+                ->shouldReceive('decrypt')
+                ->andReturn(new Assertion());
+
+            $collection = new ArrayCollection($assertions);
+            $result = $this->processor->decryptAssertions($collection);
+            self::assertInstanceOf(ArrayCollection::class, $result);
+            foreach ($result as $assertion) {
+                self::assertInstanceOf(Assertion::class, $assertion);
+            }
+        }
+    }
+
+    /**
+     * @test
+     */
+    public function unsuported_assertions_are_rejected(): void
+    {
+        $this->expectException(InvalidAssertionException::class);
+        $this->expectExceptionMessage('The assertion must be of type: EncryptedAssertion or Assertion');
+        $this->processor->decryptAssertions(new ArrayCollection([new stdClass()]));
+    }
+}