diff --git a/tests.cpp b/tests.cpp
index 2e023b5..ff0a1b9 100644
--- a/tests.cpp
+++ b/tests.cpp
@@ -289,6 +289,44 @@ void test_dynamic_cast_failure()
     assert(!derived);
 }
 
+/* Simulate a external class that cannot be modified */
+namespace external
+{
+    class Counter
+    {
+    public:
+        int start;
+        int count;
+        Counter(int start) : start(start), count(start) {}
+        virtual ~Counter() {}
+    };
+}
+
+static int external_destruct;
+
+/* Create a managed wrapper for the external class. */
+class Counter : public external::Counter
+{
+    rcp_managed_root(Counter);
+protected:
+    Counter(int start) : external::Counter(start) {}
+    ~Counter() { external_destruct++; }
+};
+
+void test_external_class()
+{
+    int before = external_destruct;
+    {
+        auto a = Counter::create(10);
+        auto b = Counter::create(20);
+        assert(a->count == 10);
+        assert(b->count == 20);
+        a->count++;
+        assert(a->count == 11);
+    }
+    assert(external_destruct == before + 2);
+}
+
 int main(int argc, char * argv[])
 {
     test_class_hierarchy();
@@ -309,5 +347,6 @@ int main(int argc, char * argv[])
     test_dynamic_cast_failure();
     test_dynamic_cast_move_success();
     test_dynamic_cast_move_failure();
+    test_external_class();
     return 0;
 }