diff --git a/library/std/src/sys/sgx/mutex.rs b/library/std/src/sys/sgx/mutex.rs
index 1b5ced4178f..8874517dac6 100644
--- a/library/std/src/sys/sgx/mutex.rs
+++ b/library/std/src/sys/sgx/mutex.rs
@@ -8,7 +8,7 @@ pub struct Mutex {
     inner: SpinMutex<WaitVariable<bool>>,
 }
 
-pub type MovableMutex = Mutex;
+pub type MovableMutex = Box<Mutex>;
 
 // Implementation according to “Operating Systems: Three Easy Pieces”, chapter 28
 impl Mutex {