diff --git a/dom/bindings/BindingUtils.h b/dom/bindings/BindingUtils.h
index 5543ceeeefc..3f46ed3fbdf 100644
--- a/dom/bindings/BindingUtils.h
+++ b/dom/bindings/BindingUtils.h
@@ -3111,6 +3111,14 @@ CreateGlobal(JSContext* aCx, T* aNative, nsWrapperCache* aCache,
     return nullptr;
   }
 
+  bool succeeded;
+  if (!JS_SetImmutablePrototype(aCx, aGlobal, &succeeded)) {
+    return nullptr;
+  }
+  MOZ_ASSERT(succeeded,
+             "making a fresh global object's [[Prototype]] immutable can "
+             "internally fail, but it should never be unsuccessful");
+
   return proto;
 }
 
diff --git a/dom/bindings/Codegen.py b/dom/bindings/Codegen.py
index 8ccab38a3c6..6459e7afd49 100644
--- a/dom/bindings/Codegen.py
+++ b/dom/bindings/Codegen.py
@@ -2953,9 +2953,32 @@ class CGCreateInterfaceObjectsMethod(CGAbstractMethod):
         else:
             unforgeableHolderSetup = None
 
+        if (self.descriptor.interface.isOnGlobalProtoChain() and
+            needInterfacePrototypeObject):
+            makeProtoPrototypeImmutable = CGGeneric(fill(
+                """
+                if (*${protoCache}) {
+                  bool succeeded;
+                  JS::Handle<JSObject*> prot = GetProtoObjectHandle(aCx, aGlobal);
+                  if (!JS_SetImmutablePrototype(aCx, prot, &succeeded)) {
+                    $*{failureCode}
+                  }
+
+                  MOZ_ASSERT(succeeded,
+                             "making a fresh prototype object's [[Prototype]] "
+                             "immutable can internally fail, but it should "
+                             "never be unsuccessful");
+                }
+                """,
+                protoCache=protoCache,
+                failureCode=failureCode))
+        else:
+            makeProtoPrototypeImmutable = None
+
         return CGList(
             [getParentProto, CGGeneric(getConstructorProto), initIds,
-             prefCache, CGGeneric(call), defineAliases, unforgeableHolderSetup],
+             prefCache, CGGeneric(call), defineAliases, unforgeableHolderSetup,
+             makeProtoPrototypeImmutable],
             "\n").define()
 
 
diff --git a/js/src/builtin/Object.cpp b/js/src/builtin/Object.cpp
index bf8ba22a300..5375da75cfb 100644
--- a/js/src/builtin/Object.cpp
+++ b/js/src/builtin/Object.cpp
@@ -1056,6 +1056,13 @@ CreateObjectPrototype(JSContext* cx, JSProtoKey key)
     if (!objectProto)
         return nullptr;
 
+    bool succeeded;
+    if (!SetImmutablePrototype(cx, objectProto, &succeeded))
+        return nullptr;
+    MOZ_ASSERT(succeeded,
+               "should have been able to make a fresh Object.prototype's "
+               "[[Prototype]] immutable");
+
     /*
      * The default 'new' type of Object.prototype is required by type inference
      * to have unknown properties, to simplify handling of e.g. heterogenous