diff --git a/wasmtime-wasi/Cargo.toml b/wasmtime-wasi/Cargo.toml
index f08ac14f74d0..7b4161cd1f70 100644
--- a/wasmtime-wasi/Cargo.toml
+++ b/wasmtime-wasi/Cargo.toml
@@ -20,6 +20,7 @@ target-lexicon = "0.3.0"
 cast = { version = "0.2.2", default-features = false }
 log = { version = "0.4.6", default-features = false }
 libc = "0.2.50"
+errno = "0.2.4"
 
 [build-dependencies]
 cmake = "0.1.35"
diff --git a/wasmtime-wasi/build.rs b/wasmtime-wasi/build.rs
index ed070ea88b4a..46d7058caf6b 100644
--- a/wasmtime-wasi/build.rs
+++ b/wasmtime-wasi/build.rs
@@ -24,7 +24,84 @@ fn main() {
         .whitelist_type("fd_table")
         .whitelist_type("fd_prestats")
         .whitelist_type("argv_environ_values")
-        .whitelist_var("__WASI_.*");
+        .whitelist_var("__WASI_.*")
+        .blacklist_item("__WASI_ESUCCESS")
+        .blacklist_item("__WASI_E2BIG")
+        .blacklist_item("__WASI_EACCES")
+        .blacklist_item("__WASI_EADDRINUSE")
+        .blacklist_item("__WASI_EADDRNOTAVAIL")
+        .blacklist_item("__WASI_EAFNOSUPPORT")
+        .blacklist_item("__WASI_EAGAIN")
+        .blacklist_item("__WASI_EALREADY")
+        .blacklist_item("__WASI_EBADF")
+        .blacklist_item("__WASI_EBADMSG")
+        .blacklist_item("__WASI_EBUSY")
+        .blacklist_item("__WASI_ECANCELED")
+        .blacklist_item("__WASI_ECHILD")
+        .blacklist_item("__WASI_ECONNABORTED")
+        .blacklist_item("__WASI_ECONNREFUSED")
+        .blacklist_item("__WASI_ECONNRESET")
+        .blacklist_item("__WASI_EDEADLK")
+        .blacklist_item("__WASI_EDESTADDRREQ")
+        .blacklist_item("__WASI_EDOM")
+        .blacklist_item("__WASI_EDQUOT")
+        .blacklist_item("__WASI_EEXIST")
+        .blacklist_item("__WASI_EFAULT")
+        .blacklist_item("__WASI_EFBIG")
+        .blacklist_item("__WASI_EHOSTUNREACH")
+        .blacklist_item("__WASI_EIDRM")
+        .blacklist_item("__WASI_EILSEQ")
+        .blacklist_item("__WASI_EINPROGRESS")
+        .blacklist_item("__WASI_EINTR")
+        .blacklist_item("__WASI_EINVAL")
+        .blacklist_item("__WASI_EIO")
+        .blacklist_item("__WASI_EISCONN")
+        .blacklist_item("__WASI_EISDIR")
+        .blacklist_item("__WASI_ELOOP")
+        .blacklist_item("__WASI_EMFILE")
+        .blacklist_item("__WASI_EMLINK")
+        .blacklist_item("__WASI_EMSGSIZE")
+        .blacklist_item("__WASI_EMULTIHOP")
+        .blacklist_item("__WASI_ENAMETOOLONG")
+        .blacklist_item("__WASI_ENETDOWN")
+        .blacklist_item("__WASI_ENETRESET")
+        .blacklist_item("__WASI_ENETUNREACH")
+        .blacklist_item("__WASI_ENFILE")
+        .blacklist_item("__WASI_ENOBUFS")
+        .blacklist_item("__WASI_ENODEV")
+        .blacklist_item("__WASI_ENOENT")
+        .blacklist_item("__WASI_ENOEXEC")
+        .blacklist_item("__WASI_ENOLCK")
+        .blacklist_item("__WASI_ENOLINK")
+        .blacklist_item("__WASI_ENOMEM")
+        .blacklist_item("__WASI_ENOMSG")
+        .blacklist_item("__WASI_ENOPROTOOPT")
+        .blacklist_item("__WASI_ENOSPC")
+        .blacklist_item("__WASI_ENOSYS")
+        .blacklist_item("__WASI_ENOTCONN")
+        .blacklist_item("__WASI_ENOTDIR")
+        .blacklist_item("__WASI_ENOTEMPTY")
+        .blacklist_item("__WASI_ENOTRECOVERABLE")
+        .blacklist_item("__WASI_ENOTSOCK")
+        .blacklist_item("__WASI_ENOTSUP")
+        .blacklist_item("__WASI_ENOTTY")
+        .blacklist_item("__WASI_ENXIO")
+        .blacklist_item("__WASI_EOVERFLOW")
+        .blacklist_item("__WASI_EOWNERDEAD")
+        .blacklist_item("__WASI_EPERM")
+        .blacklist_item("__WASI_EPIPE")
+        .blacklist_item("__WASI_EPROTO")
+        .blacklist_item("__WASI_EPROTONOSUPPORT")
+        .blacklist_item("__WASI_EPROTOTYPE")
+        .blacklist_item("__WASI_ERANGE")
+        .blacklist_item("__WASI_EROFS")
+        .blacklist_item("__WASI_ESPIPE")
+        .blacklist_item("__WASI_ESRCH")
+        .blacklist_item("__WASI_ESTALE")
+        .blacklist_item("__WASI_ETIMEDOUT")
+        .blacklist_item("__WASI_ETXTBSY")
+        .blacklist_item("__WASI_EXDEV")
+        .blacklist_item("__WASI_ENOTCAPABLE");
 
     let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());
 
diff --git a/wasmtime-wasi/sandboxed-system-primitives/include/wasmtime_ssp.h b/wasmtime-wasi/sandboxed-system-primitives/include/wasmtime_ssp.h
index 49af8252508b..7410161ee1bc 100644
--- a/wasmtime-wasi/sandboxed-system-primitives/include/wasmtime_ssp.h
+++ b/wasmtime-wasi/sandboxed-system-primitives/include/wasmtime_ssp.h
@@ -850,9 +850,6 @@ __wasi_errno_t wasmtime_ssp_sock_shutdown(
     __wasi_sdflags_t how
 ) WASMTIME_SSP_SYSCALL_NAME(sock_shutdown) __attribute__((__warn_unused_result__));
 
-__wasi_errno_t wasmtime_ssp_sched_yield(void)
-    WASMTIME_SSP_SYSCALL_NAME(sched_yield) __attribute__((__warn_unused_result__));
-
 #ifdef __cplusplus
 }
 #endif
diff --git a/wasmtime-wasi/sandboxed-system-primitives/src/posix.c b/wasmtime-wasi/sandboxed-system-primitives/src/posix.c
index 11e88fbec514..873132afcfcd 100644
--- a/wasmtime-wasi/sandboxed-system-primitives/src/posix.c
+++ b/wasmtime-wasi/sandboxed-system-primitives/src/posix.c
@@ -2684,12 +2684,6 @@ __wasi_errno_t wasmtime_ssp_sock_shutdown(
   return 0;
 }
 
-__wasi_errno_t wasmtime_ssp_sched_yield(void) {
-  if (sched_yield() < 0)
-    return convert_errno(errno);
-  return 0;
-}
-
 __wasi_errno_t wasmtime_ssp_args_get(
 #if !defined(WASMTIME_SSP_STATIC_CURFDS)
   struct argv_environ_values *argv_environ,
diff --git a/wasmtime-wasi/src/host.rs b/wasmtime-wasi/src/host.rs
index 918ea92f5eef..1b83c5491eea 100644
--- a/wasmtime-wasi/src/host.rs
+++ b/wasmtime-wasi/src/host.rs
@@ -4,3 +4,82 @@ include!(concat!(env!("OUT_DIR"), "/wasmtime_ssp.rs"));
 
 pub type char = ::std::os::raw::c_char;
 pub type void = ::std::os::raw::c_void;
+// pub type __wasi_errno_t = u16;
+
+pub const __WASI_ESUCCESS: __wasi_errno_t = 0;
+pub const __WASI_E2BIG: __wasi_errno_t = 1;
+pub const __WASI_EACCES: __wasi_errno_t = 2;
+pub const __WASI_EADDRINUSE: __wasi_errno_t = 3;
+pub const __WASI_EADDRNOTAVAIL: __wasi_errno_t = 4;
+pub const __WASI_EAFNOSUPPORT: __wasi_errno_t = 5;
+pub const __WASI_EAGAIN: __wasi_errno_t = 6;
+pub const __WASI_EALREADY: __wasi_errno_t = 7;
+pub const __WASI_EBADF: __wasi_errno_t = 8;
+pub const __WASI_EBADMSG: __wasi_errno_t = 9;
+pub const __WASI_EBUSY: __wasi_errno_t = 10;
+pub const __WASI_ECANCELED: __wasi_errno_t = 11;
+pub const __WASI_ECHILD: __wasi_errno_t = 12;
+pub const __WASI_ECONNABORTED: __wasi_errno_t = 13;
+pub const __WASI_ECONNREFUSED: __wasi_errno_t = 14;
+pub const __WASI_ECONNRESET: __wasi_errno_t = 15;
+pub const __WASI_EDEADLK: __wasi_errno_t = 16;
+pub const __WASI_EDESTADDRREQ: __wasi_errno_t = 17;
+pub const __WASI_EDOM: __wasi_errno_t = 18;
+pub const __WASI_EDQUOT: __wasi_errno_t = 19;
+pub const __WASI_EEXIST: __wasi_errno_t = 20;
+pub const __WASI_EFAULT: __wasi_errno_t = 21;
+pub const __WASI_EFBIG: __wasi_errno_t = 22;
+pub const __WASI_EHOSTUNREACH: __wasi_errno_t = 23;
+pub const __WASI_EIDRM: __wasi_errno_t = 24;
+pub const __WASI_EILSEQ: __wasi_errno_t = 25;
+pub const __WASI_EINPROGRESS: __wasi_errno_t = 26;
+pub const __WASI_EINTR: __wasi_errno_t = 27;
+pub const __WASI_EINVAL: __wasi_errno_t = 28;
+pub const __WASI_EIO: __wasi_errno_t = 29;
+pub const __WASI_EISCONN: __wasi_errno_t = 30;
+pub const __WASI_EISDIR: __wasi_errno_t = 31;
+pub const __WASI_ELOOP: __wasi_errno_t = 32;
+pub const __WASI_EMFILE: __wasi_errno_t = 33;
+pub const __WASI_EMLINK: __wasi_errno_t = 34;
+pub const __WASI_EMSGSIZE: __wasi_errno_t = 35;
+pub const __WASI_EMULTIHOP: __wasi_errno_t = 36;
+pub const __WASI_ENAMETOOLONG: __wasi_errno_t = 37;
+pub const __WASI_ENETDOWN: __wasi_errno_t = 38;
+pub const __WASI_ENETRESET: __wasi_errno_t = 39;
+pub const __WASI_ENETUNREACH: __wasi_errno_t = 40;
+pub const __WASI_ENFILE: __wasi_errno_t = 41;
+pub const __WASI_ENOBUFS: __wasi_errno_t = 42;
+pub const __WASI_ENODEV: __wasi_errno_t = 43;
+pub const __WASI_ENOENT: __wasi_errno_t = 44;
+pub const __WASI_ENOEXEC: __wasi_errno_t = 45;
+pub const __WASI_ENOLCK: __wasi_errno_t = 46;
+pub const __WASI_ENOLINK: __wasi_errno_t = 47;
+pub const __WASI_ENOMEM: __wasi_errno_t = 48;
+pub const __WASI_ENOMSG: __wasi_errno_t = 49;
+pub const __WASI_ENOPROTOOPT: __wasi_errno_t = 50;
+pub const __WASI_ENOSPC: __wasi_errno_t = 51;
+pub const __WASI_ENOSYS: __wasi_errno_t = 52;
+pub const __WASI_ENOTCONN: __wasi_errno_t = 53;
+pub const __WASI_ENOTDIR: __wasi_errno_t = 54;
+pub const __WASI_ENOTEMPTY: __wasi_errno_t = 55;
+pub const __WASI_ENOTRECOVERABLE: __wasi_errno_t = 56;
+pub const __WASI_ENOTSOCK: __wasi_errno_t = 57;
+pub const __WASI_ENOTSUP: __wasi_errno_t = 58;
+pub const __WASI_ENOTTY: __wasi_errno_t = 59;
+pub const __WASI_ENXIO: __wasi_errno_t = 60;
+pub const __WASI_EOVERFLOW: __wasi_errno_t = 61;
+pub const __WASI_EOWNERDEAD: __wasi_errno_t = 62;
+pub const __WASI_EPERM: __wasi_errno_t = 63;
+pub const __WASI_EPIPE: __wasi_errno_t = 64;
+pub const __WASI_EPROTO: __wasi_errno_t = 65;
+pub const __WASI_EPROTONOSUPPORT: __wasi_errno_t = 66;
+pub const __WASI_EPROTOTYPE: __wasi_errno_t = 67;
+pub const __WASI_ERANGE: __wasi_errno_t = 68;
+pub const __WASI_EROFS: __wasi_errno_t = 69;
+pub const __WASI_ESPIPE: __wasi_errno_t = 70;
+pub const __WASI_ESRCH: __wasi_errno_t = 71;
+pub const __WASI_ESTALE: __wasi_errno_t = 72;
+pub const __WASI_ETIMEDOUT: __wasi_errno_t = 73;
+pub const __WASI_ETXTBSY: __wasi_errno_t = 74;
+pub const __WASI_EXDEV: __wasi_errno_t = 75;
+pub const __WASI_ENOTCAPABLE: __wasi_errno_t = 76;
diff --git a/wasmtime-wasi/src/host_impls.rs b/wasmtime-wasi/src/host_impls.rs
index 8383a41372b7..a509ba25828d 100644
--- a/wasmtime-wasi/src/host_impls.rs
+++ b/wasmtime-wasi/src/host_impls.rs
@@ -1,5 +1,103 @@
+use super::host;
 use super::wasm32;
+use errno::{errno, Errno};
+
+/// Convert POSIX error code to host's WASI error code
+fn convert_errno(error: Errno) -> host::__wasi_errno_t {
+    #[allow(unreachable_patterns)]
+    match error.into() {
+        libc::E2BIG => host::__WASI_E2BIG,
+        libc::EACCES => host::__WASI_EACCES,
+        libc::EADDRINUSE => host::__WASI_EADDRINUSE,
+        libc::EADDRNOTAVAIL => host::__WASI_EADDRNOTAVAIL,
+        libc::EAFNOSUPPORT => host::__WASI_EAFNOSUPPORT,
+        libc::EAGAIN | libc::EWOULDBLOCK => host::__WASI_EAGAIN,
+        libc::EALREADY => host::__WASI_EALREADY,
+        libc::EBADF => host::__WASI_EBADF,
+        libc::EBADMSG => host::__WASI_EBADMSG,
+        libc::EBUSY => host::__WASI_EBUSY,
+        libc::ECANCELED => host::__WASI_ECANCELED,
+        libc::ECHILD => host::__WASI_ECHILD,
+        libc::ECONNABORTED => host::__WASI_ECONNABORTED,
+        libc::ECONNREFUSED => host::__WASI_ECONNREFUSED,
+        libc::ECONNRESET => host::__WASI_ECONNRESET,
+        libc::EDEADLK => host::__WASI_EDEADLK,
+        libc::EDESTADDRREQ => host::__WASI_EDESTADDRREQ,
+        libc::EDOM => host::__WASI_EDOM,
+        libc::EDQUOT => host::__WASI_EDQUOT,
+        libc::EEXIST => host::__WASI_EEXIST,
+        libc::EFAULT => host::__WASI_EFAULT,
+        libc::EFBIG => host::__WASI_EFBIG,
+        libc::EHOSTUNREACH => host::__WASI_EHOSTUNREACH,
+        libc::EIDRM => host::__WASI_EIDRM,
+        libc::EILSEQ => host::__WASI_EILSEQ,
+        libc::EINPROGRESS => host::__WASI_EINPROGRESS,
+        libc::EINTR => host::__WASI_EINTR,
+        libc::EINVAL => host::__WASI_EINVAL,
+        libc::EIO => host::__WASI_EIO,
+        libc::EISCONN => host::__WASI_EISCONN,
+        libc::EISDIR => host::__WASI_EISDIR,
+        libc::ELOOP => host::__WASI_ELOOP,
+        libc::EMFILE => host::__WASI_EMFILE,
+        libc::EMLINK => host::__WASI_EMLINK,
+        libc::EMSGSIZE => host::__WASI_EMSGSIZE,
+        libc::EMULTIHOP => host::__WASI_EMULTIHOP,
+        libc::ENAMETOOLONG => host::__WASI_ENAMETOOLONG,
+        libc::ENETDOWN => host::__WASI_ENETDOWN,
+        libc::ENETRESET => host::__WASI_ENETRESET,
+        libc::ENETUNREACH => host::__WASI_ENETUNREACH,
+        libc::ENFILE => host::__WASI_ENFILE,
+        libc::ENOBUFS => host::__WASI_ENOBUFS,
+        libc::ENODEV => host::__WASI_ENODEV,
+        libc::ENOENT => host::__WASI_ENOENT,
+        libc::ENOEXEC => host::__WASI_ENOEXEC,
+        libc::ENOLCK => host::__WASI_ENOLCK,
+        libc::ENOLINK => host::__WASI_ENOLINK,
+        libc::ENOMEM => host::__WASI_ENOMEM,
+        libc::ENOMSG => host::__WASI_ENOMSG,
+        libc::ENOPROTOOPT => host::__WASI_ENOPROTOOPT,
+        libc::ENOSPC => host::__WASI_ENOSPC,
+        libc::ENOSYS => host::__WASI_ENOSYS,
+        // TODO: verify if this is correct
+        #[cfg(target_os = "freebsd")]
+        libc::ENOTCAPABLE => host::__WASI_ENOTCAPABLE,
+        libc::ENOTCONN => host::__WASI_ENOTCONN,
+        libc::ENOTDIR => host::__WASI_ENOTDIR,
+        libc::ENOTEMPTY => host::__WASI_ENOTEMPTY,
+        libc::ENOTRECOVERABLE => host::__WASI_ENOTRECOVERABLE,
+        libc::ENOTSOCK => host::__WASI_ENOTSOCK,
+        libc::ENOTSUP | libc::EOPNOTSUPP => host::__WASI_ENOTSUP,
+        libc::ENOTTY => host::__WASI_ENOTTY,
+        libc::ENXIO => host::__WASI_ENXIO,
+        libc::EOVERFLOW => host::__WASI_EOVERFLOW,
+        libc::EOWNERDEAD => host::__WASI_EOWNERDEAD,
+        libc::EPERM => host::__WASI_EPERM,
+        libc::EPIPE => host::__WASI_EPIPE,
+        libc::EPROTO => host::__WASI_EPROTO,
+        libc::EPROTONOSUPPORT => host::__WASI_EPROTONOSUPPORT,
+        libc::EPROTOTYPE => host::__WASI_EPROTOTYPE,
+        libc::ERANGE => host::__WASI_ERANGE,
+        libc::EROFS => host::__WASI_EROFS,
+        libc::ESPIPE => host::__WASI_ESPIPE,
+        libc::ESRCH => host::__WASI_ESRCH,
+        libc::ESTALE => host::__WASI_ESTALE,
+        libc::ETIMEDOUT => host::__WASI_ETIMEDOUT,
+        libc::ETXTBSY => host::__WASI_ETXTBSY,
+        libc::EXDEV => host::__WASI_EXDEV,
+        _ => host::__WASI_ENOSYS,
+    }
+}
 
 pub fn wasmtime_ssp_proc_exit(rval: wasm32::__wasi_exitcode_t) {
     ::std::process::exit(rval as i32)
 }
+
+pub fn wasmtime_ssp_sched_yield() -> host::__wasi_errno_t {
+    unsafe {
+        if libc::sched_yield() < 0 {
+            return convert_errno(errno());
+        }
+    }
+
+    host::__WASI_ESUCCESS
+}
diff --git a/wasmtime-wasi/src/lib.rs b/wasmtime-wasi/src/lib.rs
index b6d9eb135663..d38f1d155b2f 100644
--- a/wasmtime-wasi/src/lib.rs
+++ b/wasmtime-wasi/src/lib.rs
@@ -8,6 +8,7 @@ extern crate wasmtime_jit;
 extern crate wasmtime_runtime;
 #[macro_use]
 extern crate log;
+extern crate errno;
 
 mod host;
 mod host_impls;
diff --git a/wasmtime-wasi/src/syscalls.rs b/wasmtime-wasi/src/syscalls.rs
index 7901f5531a76..4f61b4fa46d2 100644
--- a/wasmtime-wasi/src/syscalls.rs
+++ b/wasmtime-wasi/src/syscalls.rs
@@ -1413,7 +1413,7 @@ syscalls! {
     }
 
     pub unsafe extern "C" fn sched_yield(_vmctx: *mut VMContext,) -> wasm32::__wasi_errno_t {
-        let e = host::wasmtime_ssp_sched_yield();
+        let e = host_impls::wasmtime_ssp_sched_yield();
 
         return_encoded_errno(e)
     }