diff --git a/src/CachingStream.php b/src/CachingStream.php
index 2c1d65c5..7a70ee94 100644
--- a/src/CachingStream.php
+++ b/src/CachingStream.php
@@ -36,7 +36,13 @@ public function __construct(
 
     public function getSize(): ?int
     {
-        return max($this->stream->getSize(), $this->remoteStream->getSize());
+        $remoteSize = $this->remoteStream->getSize();
+
+        if (null === $remoteSize) {
+            return null;
+        }
+
+        return max($this->stream->getSize(), $remoteSize);
     }
 
     public function rewind(): void