diff --git a/dom/bindings/parser/WebIDL.py b/dom/bindings/parser/WebIDL.py
index 58d5d7e2ec23..8a001b42fa45 100644
--- a/dom/bindings/parser/WebIDL.py
+++ b/dom/bindings/parser/WebIDL.py
@@ -1082,6 +1082,10 @@ class IDLDictionary(IDLObjectWithScope):
             return (False, None)
 
         for member in self.members:
+            if member.type.isDictionary() and member.type.nullable():
+                raise WebIDLError("Dictionary %s has member with nullable "
+                                  "dictionary type" % self.identifier.name,
+                                  [member.location])
             (contains, locations) = typeContainsDictionary(member.type, self)
             if contains:
                 raise WebIDLError("Dictionary %s has member with itself as type." %
diff --git a/dom/bindings/parser/tests/test_dictionary.py b/dom/bindings/parser/tests/test_dictionary.py
index da3996f42c4c..39037168ecd0 100644
--- a/dom/bindings/parser/tests/test_dictionary.py
+++ b/dom/bindings/parser/tests/test_dictionary.py
@@ -425,3 +425,20 @@ def WebIDLTest(parser, harness):
     harness.ok(threw, "Member type must not be a Dictionary, one of whose "
                       "members or inherited members has a type that includes "
                       "its Dictionary.")
+
+    parser = parser.reset();
+    threw = False
+    try:
+        parser.parse("""
+            dictionary Foo {
+            };
+
+            dictionary Bar {
+              Foo? d;
+            };
+        """)
+        results = parser.finish()
+    except:
+        threw = True
+
+    harness.ok(threw, "Member type must not be a nullable dictionary")