diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -4755,17 +4755,17 @@ int fsconvert_strdup(PyObject *o, EXECV_
 #endif
 
 #if defined(HAVE_EXECV) || defined (HAVE_FEXECVE)
 static EXECV_CHAR**
 parse_envlist(PyObject* env, Py_ssize_t *envc_ptr)
 {
     Py_ssize_t i, pos, envc;
     PyObject *keys=NULL, *vals=NULL;
-    PyObject *key, *val, *keyval;
+    PyObject *key, *keyb, *val, *valb, *keyval;
     EXECV_CHAR **envlist;
 
     i = PyMapping_Size(env);
     if (i < 0)
         return NULL;
     envlist = PyMem_NEW(EXECV_CHAR *, i + 1);
     if (envlist == NULL) {
         PyErr_NoMemory();
@@ -4785,25 +4785,36 @@ parse_envlist(PyObject* env, Py_ssize_t 
     }
 
     for (pos = 0; pos < i; pos++) {
         key = PyList_GetItem(keys, pos);
         val = PyList_GetItem(vals, pos);
         if (!key || !val)
             goto error;
 
+#ifndef MS_WINDOWS
+        if (!PyUnicode_FSConverter(key, &keyb))
+            goto error;
+        if (!PyUnicode_FSConverter(val, &valb))
+            goto error;
+        keyval = PyBytes_FromFormat("%s=%s",
+                                    PyBytes_AsString(keyb),
+                                    PyBytes_AsString(valb));
+#else
         keyval = PyUnicode_FromFormat("%U=%U", key, val);
+#endif
         if (!keyval)
             goto error;
 
         if (!fsconvert_strdup(keyval, &envlist[envc++])) {
             Py_DECREF(keyval);
             goto error;
         }
-        
+        Py_DECREF(keyb);
+        Py_DECREF(valb);
         Py_DECREF(keyval);
     }
     Py_DECREF(vals);
     Py_DECREF(keys);
 
     envlist[envc] = 0;
     *envc_ptr = envc;
     return envlist;