diff --git a/js/src/builtin/ModuleObject.cpp b/js/src/builtin/ModuleObject.cpp
index 92ca19bdee7..fd83fccea9b 100644
--- a/js/src/builtin/ModuleObject.cpp
+++ b/js/src/builtin/ModuleObject.cpp
@@ -941,8 +941,9 @@ bool ModuleObject::isInstance(HandleValue value) {
 }
 
 bool ModuleObject::hasCyclicModuleFields() const {
-  // This currently only returns false if we GC during initialization.
-  return !getReservedSlot(CyclicModuleFieldsSlot).isUndefined();
+  bool result = !getReservedSlot(CyclicModuleFieldsSlot).isUndefined();
+  MOZ_ASSERT_IF(result, !hasSyntheticModuleFields());
+  return result;
 }
 
 CyclicModuleFields* ModuleObject::cyclicModuleFields() {
@@ -1482,7 +1483,9 @@ bool ModuleObject::createSyntheticEnvironment(JSContext* cx,
     return false;
   }
 
-  MOZ_ASSERT(env->shape()->propMapLength() == values.length());
+  // We expect one property per synthetic value plus one for the *namespace*
+  // binding.
+  MOZ_ASSERT(env->shape()->propMapLength() == values.length() + 1);
 
   for (uint32_t i = 0; i < values.length(); i++) {
     env->setAliasedBinding(env->firstSyntheticValueSlot() + i, values[i]);
diff --git a/js/src/vm/EnvironmentObject.h b/js/src/vm/EnvironmentObject.h
index e9dd45027e5..b5c044987e1 100644
--- a/js/src/vm/EnvironmentObject.h
+++ b/js/src/vm/EnvironmentObject.h
@@ -773,7 +773,7 @@ class ModuleEnvironmentObject : public EnvironmentObject {
   // `env` may be a DebugEnvironmentProxy, but not a hollow environment.
   static ModuleEnvironmentObject* find(JSObject* env);
 
-  uint32_t firstSyntheticValueSlot() { return RESERVED_SLOTS; }
+  uint32_t firstSyntheticValueSlot() { return RESERVED_SLOTS + 1; }
 
  private:
   static bool lookupProperty(JSContext* cx, HandleObject obj, HandleId id,
diff --git a/js/src/vm/Modules.cpp b/js/src/vm/Modules.cpp
index b6e57fc7403..24df191b61f 100644
--- a/js/src/vm/Modules.cpp
+++ b/js/src/vm/Modules.cpp
@@ -1705,8 +1705,9 @@ static bool InnerModuleLinking(JSContext* cx, Handle<ModuleObject*> module,
                                size_t* indexOut) {
   // Step 1. If module is not a Cyclic Module Record, then
   if (!module->hasCyclicModuleFields()) {
-    // Step 1.a. Perform ? module.Link(). (Skipped)
-    // Step 2.b. Return index.
+    // Step 1.a. Perform ? module.Link().
+    // (Skipped as we have already created the environment for these modules).
+    // Step 1.b. Return index.
     *indexOut = index;
     return true;
   }
diff --git a/js/src/vm/Scope.cpp b/js/src/vm/Scope.cpp
index 155a0025ebd..ac515c0d123 100644
--- a/js/src/vm/Scope.cpp
+++ b/js/src/vm/Scope.cpp
@@ -161,11 +161,22 @@ SharedShape* js::CreateEnvironmentShapeForSyntheticModule(
 
   RootedId id(cx);
   uint32_t slotIndex = numSlots;
+
+  auto addProperty = [&](PropertyName* name) {
+    id = NameToId(name);
+    return SharedPropMap::addPropertyWithKnownSlot(
+        cx, cls, &map, &mapLength, id, propFlags, slotIndex, &objectFlags);
+  };
+
+  // Add internal *namespace* property.
+  if (!addProperty(cx->names().star_namespace_star_)) {
+    return nullptr;
+  }
+  slotIndex++;
+
+  // Add synthetic exports.
   for (JSAtom* exportName : module->syntheticExportNames()) {
-    id = NameToId(exportName->asPropertyName());
-    if (!SharedPropMap::addPropertyWithKnownSlot(cx, cls, &map, &mapLength, id,
-                                                 propFlags, slotIndex,
-                                                 &objectFlags)) {
+    if (!addProperty(exportName->asPropertyName())) {
       return nullptr;
     }
     slotIndex++;