diff --git a/components/script/dom/bindings/codegen/CodegenRust.py b/components/script/dom/bindings/codegen/CodegenRust.py
index b833d431f7f..e7fcb887782 100644
--- a/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/components/script/dom/bindings/codegen/CodegenRust.py
@@ -1409,8 +1409,7 @@ class PropertyDefiner:
         assert len(array) != 0
         specs = []
         prefableSpecs = []
-        prefableTemplate = '    Prefable { pref: %s, specs: %s[%d], terminator: %s }'
-        hasTerminator = 'true' if specTerminator else 'false'
+        prefableTemplate = '    Prefable { pref: %s, specs: %s[%d] }'
 
         for cond, members in groupby(array, lambda m: getCondition(m, self.descriptor)):
             currentSpecs = [specTemplate % getDataTuple(m) for m in members]
@@ -1418,7 +1417,7 @@ class PropertyDefiner:
                 currentSpecs.append(specTerminator)
             specs.append("&[\n" + ",\n".join(currentSpecs) + "]\n")
             prefableSpecs.append(
-                prefableTemplate % (cond, name + "_specs", len(specs) - 1, hasTerminator))
+                prefableTemplate % (cond, name + "_specs", len(specs) - 1))
 
         specsArray = ("const %s_specs: &'static [&'static[%s]] = &[\n" +
                       ",\n".join(specs) + "\n" +
diff --git a/components/script/dom/bindings/interface.rs b/components/script/dom/bindings/interface.rs
index f1e6a886eb7..8791cd4da08 100644
--- a/components/script/dom/bindings/interface.rs
+++ b/components/script/dom/bindings/interface.rs
@@ -216,7 +216,9 @@ pub unsafe fn create_callback_interface_object(
     rval.set(JS_NewObject(cx, ptr::null()));
     assert!(!rval.ptr.is_null());
     for prefable in constants {
-        define_constants(cx, rval.handle(), prefable.specs());
+        if let Some(specs) = prefable.specs() {
+            define_constants(cx, rval.handle(), specs);
+        }
     }
     define_name(cx, rval.handle(), name);
     define_on_global_object(cx, receiver, name, rval.handle());
@@ -363,7 +365,9 @@ unsafe fn create_object(
     define_prefable_methods(cx, rval.handle(), methods);
     define_prefable_properties(cx, rval.handle(), properties);
     for prefable in constants {
-        define_constants(cx, rval.handle(), prefable.specs());
+        if let Some(specs) = prefable.specs() {
+            define_constants(cx, rval.handle(), specs);
+        }
     }
 }
 
@@ -373,7 +377,9 @@ pub unsafe fn define_prefable_methods(
         obj: HandleObject,
         methods: &'static [Prefable<JSFunctionSpec>]) {
     for prefable in methods {
-        define_methods(cx, obj, prefable.specs()).unwrap();
+        if let Some(specs) = prefable.specs() {
+            define_methods(cx, obj, specs).unwrap();
+        }
     }
 }
 
@@ -383,7 +389,9 @@ pub unsafe fn define_prefable_properties(
         obj: HandleObject,
         properties: &'static [Prefable<JSPropertySpec>]) {
     for prefable in properties {
-        define_properties(cx, obj, prefable.specs()).unwrap();
+        if let Some(specs) = prefable.specs() {
+            define_properties(cx, obj, specs).unwrap();
+        }
     }
 }
 
diff --git a/components/script/dom/bindings/utils.rs b/components/script/dom/bindings/utils.rs
index 607f74456d2..3ba5838a4fa 100644
--- a/components/script/dom/bindings/utils.rs
+++ b/components/script/dom/bindings/utils.rs
@@ -557,24 +557,17 @@ pub struct Prefable<T: 'static> {
     pub pref: Option<&'static str>,
     /// The underlying slice of specifications.
     pub specs: &'static [T],
-    /// Whether the specifications contain special terminating entries that should be
-    /// included or not.
-    pub terminator: bool,
 }
 
 impl<T> Prefable<T> {
     /// Retrieve the slice represented by this container, unless the condition
     /// guarding it is false.
-    pub fn specs(&self) -> &'static [T] {
+    pub fn specs(&self) -> Option<&'static [T]> {
         if let Some(pref) = self.pref {
             if !prefs::get_pref(pref).as_boolean().unwrap_or(false) {
-                return if self.terminator {
-                    &self.specs[self.specs.len() - 1..]
-                } else {
-                    &[]
-                };
+                return None;
             }
         }
-        self.specs
+        Some(self.specs)
     }
 }