diff --git a/src/Stream.php b/src/Stream.php
index 96c0982e..c6de0458 100644
--- a/src/Stream.php
+++ b/src/Stream.php
@@ -364,4 +364,11 @@ private function isValidStreamResourceType(mixed $resource): bool
 
         return false;
     }
+
+    /**
+     * Disallow stream cloning.
+     */
+    private function __clone()
+    {
+    }
 }
diff --git a/test/StreamTest.php b/test/StreamTest.php
index 245d7bde..0503222d 100644
--- a/test/StreamTest.php
+++ b/test/StreamTest.php
@@ -5,6 +5,7 @@
 namespace LaminasTest\Diactoros;
 
 use CurlHandle;
+use Error;
 use GdImage;
 use InvalidArgumentException;
 use Laminas\Diactoros\Stream;
@@ -679,4 +680,18 @@ public function testSizeReportsNullForPhpInputStreams(): void
         $stream   = new Stream($resource);
         $this->assertNull($stream->getSize());
     }
+
+    public function testStreamsAreUnclonable(): void
+    {
+        $stream = new Stream(fopen('php://temp', 'r+'));
+        $stream->write('foo');
+
+        $this->assertSame('foo', $stream->__toString());
+
+        $this->expectException(Error::class);
+        $this->expectExceptionMessage('private Laminas\Diactoros\Stream::__clone()');
+
+        /** @psalm-suppress InvalidClone */
+        clone $stream;
+    }
 }