diff --git a/Lib/test/test_compileall.py b/Lib/test/test_compileall.py
index 38d7b996c7c221..0a07bb29b34319 100644
--- a/Lib/test/test_compileall.py
+++ b/Lib/test/test_compileall.py
@@ -555,6 +555,30 @@ def test_workers_available_cores(self, compile_dir):
             self.assertTrue(compile_dir.called)
             self.assertEqual(compile_dir.call_args[-1]['workers'], None)
 
+    def test_deterministic_serialization(self):
+        # http://bugs.python.org/issue34722
+        # We have to test this in subprocesses since the nondeterminism
+        # revolves around the hash seed.
+        with open(os.path.join(self.pkgdir, 'set.py'), 'w') as f:
+            f.write("def test(x):\n")
+            f.write("    if x in {'ONE', 'TWO', 'THREE'}:\n")
+            f.write("        pass\n")
+
+        def compile_dir():
+            self.assertRunOK(
+                '-q',
+                '--invalidation-mode=unchecked-hash',
+                self.pkgdir,
+            )
+            for file in sorted(os.listdir(self.pkgdir_cachedir)):
+                with open(os.path.join(self.pkgdir_cachedir, file), 'rb') as f:
+                    yield f.read()
+
+        serialized = list(compile_dir())
+        for _ in range(5):
+            shutil.rmtree(self.pkgdir_cachedir)
+            self.assertEqual(serialized, list(compile_dir()))
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/Misc/NEWS.d/next/Core and Builtins/2018-09-21-15-38-47.bpo-34722.F6VE5R.rst b/Misc/NEWS.d/next/Core and Builtins/2018-09-21-15-38-47.bpo-34722.F6VE5R.rst
new file mode 100644
index 00000000000000..509c052aa1fa60
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2018-09-21-15-38-47.bpo-34722.F6VE5R.rst	
@@ -0,0 +1,4 @@
+Ensures that sets / frozensets marshal in a consistent order by sorting the
+serialised items before writing them. This will result in somewhat slower
+serialisation but bytecode files using set literals in certain contexts will
+now serialise deterministically where it didn't before.
diff --git a/Python/marshal.c b/Python/marshal.c
index 21cdd60c7e1377..0455c1f8ff9f81 100644
--- a/Python/marshal.c
+++ b/Python/marshal.c
@@ -496,7 +496,7 @@ w_complex_object(PyObject *v, char flag, WFILE *p)
         w_object((PyObject *)NULL, p);
     }
     else if (PyAnySet_CheckExact(v)) {
-        PyObject *value, *it;
+        PyObject *value, *l;
 
         if (PyObject_TypeCheck(v, &PySet_Type))
             W_TYPE(TYPE_SET, p);
@@ -509,17 +509,27 @@ w_complex_object(PyObject *v, char flag, WFILE *p)
             return;
         }
         W_SIZE(n, p);
-        it = PyObject_GetIter(v);
-        if (it == NULL) {
+        l = PySequence_List(v);
+        if (l == NULL) {
             p->depth--;
             p->error = WFERR_UNMARSHALLABLE;
             return;
         }
-        while ((value = PyIter_Next(it)) != NULL) {
-            w_object(value, p);
-            Py_DECREF(value);
+        for (i = 0; i < n; i++) {
+            value = PyList_GetItem(l, i);
+            value = PyMarshal_WriteObjectToString(value, Py_MARSHAL_VERSION);
+            PyList_SetItem(l, i, value);
+        }
+        if (PyList_Sort(l) == -1) {
+            Py_DECREF(l);
+            p->depth--;
+            p->error = WFERR_UNMARSHALLABLE;
+            return;
+        }
+        for (i = 0; i < n; i++) {
+            w_object(PyList_GetItem(l, i), p);
         }
-        Py_DECREF(it);
+        Py_DECREF(l);
         if (PyErr_Occurred()) {
             p->depth--;
             p->error = WFERR_UNMARSHALLABLE;