diff --git a/src/Io/EmptyBodyStream.v2.php b/src/Io/EmptyBodyStream.v2.php
index 4b59c29c..f92abbba 100644
--- a/src/Io/EmptyBodyStream.v2.php
+++ b/src/Io/EmptyBodyStream.v2.php
@@ -136,7 +136,7 @@ public function getContents(): string
     }
 
     /** @ignore */
-    public function getMetadata($key = null)
+    public function getMetadata(?string $key = null)
     {
         return ($key === null) ? array() : null;
     }
diff --git a/src/Io/HttpBodyStream.v2.php b/src/Io/HttpBodyStream.v2.php
index 800007d9..ae9f1a93 100644
--- a/src/Io/HttpBodyStream.v2.php
+++ b/src/Io/HttpBodyStream.v2.php
@@ -154,7 +154,7 @@ public function getContents(): string
     }
 
     /** @ignore */
-    public function getMetadata($key = null)
+    public function getMetadata(?string $key = null)
     {
         return null;
     }