diff --git a/artiq/test/serialization.py b/artiq/test/serialization.py
index 9c23481b9..841010df8 100644
--- a/artiq/test/serialization.py
+++ b/artiq/test/serialization.py
@@ -10,7 +10,7 @@ from artiq.protocols import pyon
 _pyon_test_object = {
     (1, 2): [(3, 4.2), (2, )],
     Fraction(3, 4): np.linspace(5, 10, 1),
-    {"testing", "sets"},
+    "set": {"testing", "sets"},
     "a": np.int8(9), "b": np.int16(-98), "c": np.int32(42), "d": np.int64(-5),
     "e": np.uint8(8), "f": np.uint16(5), "g": np.uint32(4), "h": np.uint64(9),
     "x": np.float16(9.0), "y": np.float32(9.0), "z": np.float64(9.0),