diff -r 000000000000 -r 6474c204b198 dom/bindings/parser/tests/test_union_nullable.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/bindings/parser/tests/test_union_nullable.py	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,53 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse("""
+            interface OneNullableInUnion {
+              void foo((object? or DOMString?) arg);
+            };
+        """)
+
+        results = parser.finish()
+    except:
+        threw = True
+
+    harness.ok(threw,
+               "Two nullable member types of a union should have thrown.")
+
+    parser.reset()
+    threw = False
+
+    try:
+        parser.parse("""
+            interface NullableInNullableUnion {
+              void foo((object? or DOMString)? arg);
+            };
+        """)
+
+        results = parser.finish()
+    except:
+        threw = True
+
+    harness.ok(threw,
+               "A nullable union type with a nullable member type should have "
+               "thrown.")
+
+    parser.reset()
+    threw = False
+
+    try:
+        parser.parse("""
+            interface NullableInUnionNullableUnionHelper {
+            };
+            interface NullableInUnionNullableUnion {
+              void foo(((object? or DOMString) or NullableInUnionNullableUnionHelper)? arg);
+            };
+        """)
+
+        results = parser.finish()
+    except:
+        threw = True
+
+    harness.ok(threw,
+               "A nullable union type with a nullable member type should have "
+               "thrown.")