diff --git a/document/js-api/index.bs b/document/js-api/index.bs
index 01dfc58e..077f9435 100644
--- a/document/js-api/index.bs
+++ b/document/js-api/index.bs
@@ -335,11 +335,11 @@ dictionary WebAssemblyCompileOptions {
 
 [Exposed=*]
 namespace WebAssembly {
-    boolean validate(BufferSource bytes, optional WebAssemblyCompileOptions options);
-    Promise<Module> compile(BufferSource bytes, optional WebAssemblyCompileOptions options);
+    boolean validate(BufferSource bytes, optional WebAssemblyCompileOptions options = {});
+    Promise<Module> compile(BufferSource bytes, optional WebAssemblyCompileOptions options = {});
 
     Promise<WebAssemblyInstantiatedSource> instantiate(
-        BufferSource bytes, optional object importObject, optional WebAssemblyCompileOptions options);
+        BufferSource bytes, optional object importObject, optional WebAssemblyCompileOptions options = {});
 
     Promise<Instance> instantiate(
         Module moduleObject, optional object importObject);
@@ -653,7 +653,7 @@ dictionary ModuleImportDescriptor {
 
 [LegacyNamespace=WebAssembly, Exposed=*]
 interface Module {
-  constructor(BufferSource bytes, optional WebAssemblyCompileOptions options);
+  constructor(BufferSource bytes, optional WebAssemblyCompileOptions options = {});
   static sequence<ModuleExportDescriptor> exports(Module moduleObject);
   static sequence<ModuleImportDescriptor> imports(Module moduleObject);
   static sequence<ArrayBuffer> customSections(Module moduleObject, DOMString sectionName);