diff --git a/src/libstd/os/mod.rs b/src/libstd/os/mod.rs
index 91e37ed833a4f..0fa4a1d2353ca 100644
--- a/src/libstd/os/mod.rs
+++ b/src/libstd/os/mod.rs
@@ -24,7 +24,7 @@ cfg_if::cfg_if! {
         // If we're not documenting libstd then we just expose the main modules
         // as we otherwise would.
 
-        #[cfg(any(target_os = "redox", unix, target_os = "vxworks"))]
+        #[cfg(any(target_os = "redox", unix, target_os = "vxworks", target_os = "hermit"))]
         #[stable(feature = "rust1", since = "1.0.0")]
         pub use crate::sys::ext as unix;
 
diff --git a/src/libstd/sys/hermit/ext/ffi.rs b/src/libstd/sys/hermit/ext/ffi.rs
new file mode 100644
index 0000000000000..07b59a02556d9
--- /dev/null
+++ b/src/libstd/sys/hermit/ext/ffi.rs
@@ -0,0 +1,38 @@
+//! HermitCore-specific extension to the primitives in the `std::ffi` module
+//!
+//! # Examples
+//!
+//! ```
+//! use std::ffi::OsString;
+//! use std::os::hermit::ffi::OsStringExt;
+//!
+//! let bytes = b"foo".to_vec();
+//!
+//! // OsStringExt::from_vec
+//! let os_string = OsString::from_vec(bytes);
+//! assert_eq!(os_string.to_str(), Some("foo"));
+//!
+//! // OsStringExt::into_vec
+//! let bytes = os_string.into_vec();
+//! assert_eq!(bytes, b"foo");
+//! ```
+//!
+//! ```
+//! use std::ffi::OsStr;
+//! use std::os::hermit::ffi::OsStrExt;
+//!
+//! let bytes = b"foo";
+//!
+//! // OsStrExt::from_bytes
+//! let os_str = OsStr::from_bytes(bytes);
+//! assert_eq!(os_str.to_str(), Some("foo"));
+//!
+//! // OsStrExt::as_bytes
+//! let bytes = os_str.as_bytes();
+//! assert_eq!(bytes, b"foo");
+//! ```
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use crate::sys_common::os_str_bytes::*;
diff --git a/src/libstd/sys/hermit/ext/mod.rs b/src/libstd/sys/hermit/ext/mod.rs
new file mode 100644
index 0000000000000..ea87d0ad2c94d
--- /dev/null
+++ b/src/libstd/sys/hermit/ext/mod.rs
@@ -0,0 +1,14 @@
+#![stable(feature = "rust1", since = "1.0.0")]
+#![allow(missing_docs)]
+
+pub mod ffi;
+
+/// A prelude for conveniently writing platform-specific code.
+///
+/// Includes all extension traits, and some important type definitions.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub mod prelude {
+    #[doc(no_inline)]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub use super::ffi::{OsStrExt, OsStringExt};
+}
diff --git a/src/libstd/sys/hermit/mod.rs b/src/libstd/sys/hermit/mod.rs
index 1e4a53abdc7bd..362461ce97acd 100644
--- a/src/libstd/sys/hermit/mod.rs
+++ b/src/libstd/sys/hermit/mod.rs
@@ -21,6 +21,7 @@ pub mod args;
 pub mod cmath;
 pub mod condvar;
 pub mod env;
+pub mod ext;
 pub mod fast_thread_local;
 pub mod fd;
 pub mod fs;