diff --git a/src/core/thread/osthread.d b/src/core/thread/osthread.d
index c1b25d2a9d..2915225865 100644
--- a/src/core/thread/osthread.d
+++ b/src/core/thread/osthread.d
@@ -983,7 +983,7 @@ class Thread : ThreadBase
     }
 }
 
-private Thread toThread(ThreadBase t) @trusted nothrow @nogc pure
+private Thread toThread(return scope ThreadBase t) @trusted nothrow @nogc pure
 {
     return cast(Thread) cast(void*) t;
 }