diff --git a/src/wasi.rs b/src/wasi.rs
index 429bc53f..bd2cbfa1 100644
--- a/src/wasi.rs
+++ b/src/wasi.rs
@@ -138,7 +138,8 @@ s! {
     }
 
     pub struct fd_set {
-        fds_bits: [c_ulong; FD_SETSIZE / ULONG_SIZE],
+        pub __nfds: size_t,
+        pub __fds: [c_int; FD_SETSIZE],
     }
 
     pub struct lconv {