diff -r 000000000000 -r 6474c204b198 dom/bindings/parser/tests/test_optional_constraints.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/bindings/parser/tests/test_optional_constraints.py	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,30 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse("""
+            interface OptionalConstraints1 {
+              void foo(optional byte arg1, byte arg2);
+            };
+        """)
+
+        results = parser.finish()
+    except:
+        threw = True
+
+    harness.ok(not threw,
+               "Should not have thrown on non-optional argument following "
+               "optional argument.")
+
+    parser = parser.reset()
+    parser.parse("""
+        interface OptionalConstraints2 {
+          void foo(optional byte arg1 = 1, optional byte arg2 = 2,
+                   optional byte arg3, optional byte arg4 = 4,
+                   optional byte arg5, optional byte arg6 = 9);
+        };
+    """)
+    results = parser.finish()
+    args = results[0].members[0].signatures()[0][1]
+    harness.check(len(args), 6, "Should have 6 arguments")
+    harness.check(args[5].defaultValue.value, 9,
+                  "Should have correct default value")