diff --git a/vm/src/stdlib/os.rs b/vm/src/stdlib/os.rs
index 0c1f240d79..e890929657 100644
--- a/vm/src/stdlib/os.rs
+++ b/vm/src/stdlib/os.rs
@@ -26,7 +26,8 @@ use crate::obj::objset::PySet;
 use crate::obj::objstr::{self, PyString, PyStringRef};
 use crate::obj::objtype::{self, PyClassRef};
 use crate::pyobject::{
-    ItemProtocol, PyClassImpl, PyObjectRef, PyRef, PyResult, PyValue, TryIntoRef, TypeProtocol,
+    Either, ItemProtocol, PyClassImpl, PyObjectRef, PyRef, PyResult, PyValue, TryIntoRef,
+    TypeProtocol,
 };
 use crate::vm::VirtualMachine;
 
@@ -416,12 +417,46 @@ fn os_listdir(path: PyStringRef, vm: &VirtualMachine) -> PyResult {
     }
 }
 
-fn os_putenv(key: PyStringRef, value: PyStringRef, _vm: &VirtualMachine) {
-    env::set_var(&key.value, &value.value)
+fn bytes_as_osstr<'a>(b: &'a [u8], vm: &VirtualMachine) -> PyResult<&'a ffi::OsStr> {
+    let os_str = {
+        #[cfg(unix)]
+        {
+            use std::os::unix::ffi::OsStrExt;
+            Some(ffi::OsStr::from_bytes(b))
+        }
+        #[cfg(windows)]
+        {
+            std::str::from_utf8(b).ok().map(|s| s.as_ref())
+        }
+    };
+    os_str
+        .ok_or_else(|| vm.new_value_error("Can't convert bytes to str for env function".to_owned()))
 }
 
-fn os_unsetenv(key: PyStringRef, _vm: &VirtualMachine) {
-    env::remove_var(&key.value)
+fn os_putenv(
+    key: Either<PyStringRef, PyBytesRef>,
+    value: Either<PyStringRef, PyBytesRef>,
+    vm: &VirtualMachine,
+) -> PyResult<()> {
+    let key: &ffi::OsStr = match key {
+        Either::A(ref s) => s.as_str().as_ref(),
+        Either::B(ref b) => bytes_as_osstr(b.get_value(), vm)?,
+    };
+    let value: &ffi::OsStr = match value {
+        Either::A(ref s) => s.as_str().as_ref(),
+        Either::B(ref b) => bytes_as_osstr(b.get_value(), vm)?,
+    };
+    env::set_var(key, value);
+    Ok(())
+}
+
+fn os_unsetenv(key: Either<PyStringRef, PyBytesRef>, vm: &VirtualMachine) -> PyResult<()> {
+    let key: &ffi::OsStr = match key {
+        Either::A(ref s) => s.as_str().as_ref(),
+        Either::B(ref b) => bytes_as_osstr(b.get_value(), vm)?,
+    };
+    env::remove_var(key);
+    Ok(())
 }
 
 fn _os_environ(vm: &VirtualMachine) -> PyDictRef {