diff --git a/src/unix/bsd/apple/b64/aarch64/align.rs b/src/unix/bsd/apple/b64/aarch64/align.rs
index 131e15b69ad94..29db97ec7c473 100644
--- a/src/unix/bsd/apple/b64/aarch64/align.rs
+++ b/src/unix/bsd/apple/b64/aarch64/align.rs
@@ -15,6 +15,7 @@ s! {
         pub uc_link: *mut ::ucontext_t,
         pub uc_mcsize: usize,
         pub uc_mcontext: mcontext_t,
+        __mcontext_data: __darwin_mcontext64,
     }
 
     pub struct __darwin_mcontext64 {