diff --git a/scripts/qapi.py b/scripts/qapi.py
index 78db319831..f4c82100f4 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -735,7 +735,7 @@ def check_union(expr, info):
             raise QAPISemError(info, "Flat union '%s' must have a base"
                                % name)
         base_members = find_base_members(base)
-        assert base_members
+        assert base_members is not None
 
         # The value of member 'discriminator' must name a non-optional
         # member of the base struct.
diff --git a/tests/qapi-schema/union-base-empty.err b/tests/qapi-schema/union-base-empty.err
index 26bfa07bc9..7695806d81 100644
--- a/tests/qapi-schema/union-base-empty.err
+++ b/tests/qapi-schema/union-base-empty.err
@@ -1,10 +1 @@
-Traceback (most recent call last):
-  File "tests/qapi-schema/test-qapi.py", line 56, in <module>
-    schema = QAPISchema(sys.argv[1])
-  File "scripts/qapi.py", line 1487, in __init__
-    self.exprs = check_exprs(parser.exprs)
-  File "scripts/qapi.py", line 921, in check_exprs
-    check_union(expr, info)
-  File "scripts/qapi.py", line 738, in check_union
-    assert base_members
-AssertionError
+tests/qapi-schema/union-base-empty.json:5: Discriminator 'type' is not a member of base struct 'Empty'