diff --git a/src/libstd/sys/unix/io.rs b/src/libstd/sys/unix/io.rs
index 72954ff20ef9..bc854e772e16 100644
--- a/src/libstd/sys/unix/io.rs
+++ b/src/libstd/sys/unix/io.rs
@@ -29,6 +29,7 @@ impl<'a> IoSlice<'a> {
     }
 }
 
+#[repr(transparent)]
 pub struct IoSliceMut<'a> {
     vec: iovec,
     _p: PhantomData<&'a mut [u8]>,
diff --git a/src/libstd/sys/wasi/io.rs b/src/libstd/sys/wasi/io.rs
index cc8f1e16fa01..a5bddad708b1 100644
--- a/src/libstd/sys/wasi/io.rs
+++ b/src/libstd/sys/wasi/io.rs
@@ -29,6 +29,7 @@ impl<'a> IoSlice<'a> {
     }
 }
 
+#[repr(transparent)]
 pub struct IoSliceMut<'a> {
     vec: __wasi_iovec_t,
     _p: PhantomData<&'a mut [u8]>,
diff --git a/src/libstd/sys/windows/io.rs b/src/libstd/sys/windows/io.rs
index c045a63e9118..f0da2323f4f5 100644
--- a/src/libstd/sys/windows/io.rs
+++ b/src/libstd/sys/windows/io.rs
@@ -29,6 +29,7 @@ impl<'a> IoSlice<'a> {
     }
 }
 
+#[repr(transparent)]
 pub struct IoSliceMut<'a> {
     vec: c::WSABUF,
     _p: PhantomData<&'a mut [u8]>,