diff --git a/src/wuttaweb/util.py b/src/wuttaweb/util.py
index 1080820..a708398 100644
--- a/src/wuttaweb/util.py
+++ b/src/wuttaweb/util.py
@@ -654,6 +654,13 @@ def make_json_safe(value, key=None, warn=True):
             parent[i] = make_json_safe(v, key=key, warn=warn)
         value = parent
 
+    elif isinstance(value, set):
+        # recursively convert set (as list)
+        parent = list(value)
+        for i, v in enumerate(parent):
+            parent[i] = make_json_safe(v, key=key, warn=warn)
+        value = parent
+
     elif isinstance(value, _uuid.UUID):
         # convert UUID to str
         value = value.hex
diff --git a/tests/test_util.py b/tests/test_util.py
index 0be2911..b9c7490 100644
--- a/tests/test_util.py
+++ b/tests/test_util.py
@@ -735,6 +735,30 @@ class TestMakeJsonSafe(TestCase):
             ],
         )
 
+    def test_set(self):
+        model = self.app.model
+        person = model.Person(full_name="Betty Boop")
+
+        data = {
+            "foo",
+            "bar",
+            person,
+        }
+
+        self.assertRaises(TypeError, json.dumps, data)
+        value = mod.make_json_safe(data)
+        self.assertNotIsInstance(value, set)
+        self.assertIsInstance(value, list)
+        # nb. must sort values, otherwise comparison may fail
+        self.assertEqual(
+            sorted(value),
+            [
+                "Betty Boop",  # nb. upper-case sorts first
+                "bar",
+                "foo",
+            ],
+        )
+
 
 class TestRenderVueFinalize(TestCase):