diff --git a/components/script/dom/bindings/codegen/CodegenRust.py b/components/script/dom/bindings/codegen/CodegenRust.py
index 1bd01651e762..fe88275bf20e 100644
--- a/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/components/script/dom/bindings/codegen/CodegenRust.py
@@ -747,7 +747,15 @@ def wrapObjectTemplate(templateBody, nullValue, isDefinitelyObject, type,
             for memberType in type.unroll().flatMemberTypes
             if memberType.isDictionary()
         ]
-        if dictionaries:
+        if defaultValue and not isinstance(defaultValue, IDLNullValue):
+            tag = defaultValue.type.tag()
+            if tag is IDLType.Tags.bool:
+                default = "%s::Boolean(%s)" % (
+                    union_native_type(type),
+                    "true" if defaultValue.value else "false")
+            else:
+                raise("We don't currently support default values that aren't null or boolean")
+        elif dictionaries:
             if defaultValue:
                 assert isinstance(defaultValue, IDLNullValue)
                 dictionary, = dictionaries
diff --git a/components/script/dom/webidls/MediaDevices.webidl b/components/script/dom/webidls/MediaDevices.webidl
index e439a80c5129..866e1e964d0c 100644
--- a/components/script/dom/webidls/MediaDevices.webidl
+++ b/components/script/dom/webidls/MediaDevices.webidl
@@ -23,10 +23,8 @@ partial interface MediaDevices {
 
 
 dictionary MediaStreamConstraints {
-        (boolean or MediaTrackConstraints) video;
-        // (boolean or MediaTrackConstraints) video = false;
-        (boolean or MediaTrackConstraints) audio;
-        // (boolean or MediaTrackConstraints) audio = false;
+        (boolean or MediaTrackConstraints) video = false;
+        (boolean or MediaTrackConstraints) audio = false;
 };
 
 dictionary DoubleRange {