diff --git a/stub-ext/stubext.h b/stub-ext/stubext.h
index 5ddf5aa9db7b0007224817c5bd29c48c36bd93da..071070ca047dc6a0a5282afd337d937932889dbe 100644
--- a/stub-ext/stubext.h
+++ b/stub-ext/stubext.h
@@ -42,25 +42,30 @@ public:
     StubExt() : Stub() {}
 
     template<typename T, class Lamda>
-    void set_lamda(T addr, Lamda lamda)
+    bool set_lamda(T addr, Lamda lamda)
     {
+        char *fn = reinterpret_cast<char*>(addrof(addr));
+        if (m_result.find(fn) != m_result.end()) {
+            assert(m_result.find(fn) == m_result.end());
+            return false;
+        }
+
         Wrapper *wrapper = nullptr;
         auto addr_stub = depictShadow(&wrapper,addr,lamda);
-        set(addr, addr_stub);
-        char *fn = addrof(addr);
-        auto iter = m_result.find(fn);
-        if (iter != m_result.end()) {
-            m_wrappers.insert(std::make_pair(fn,wrapper));
+        if (set(addr, addr_stub)) {
+            m_wrappers.insert(std::make_pair(fn, wrapper));
+            return true;
         } else {
             freeWrapper(wrapper);
         }
+        return false;
     }
 
     template<typename T>
     void reset(T addr)
     {
         Stub::reset(addr);
-        char *fn = addrof(addr);
+        char *fn = reinterpret_cast<char*>(addrof(addr));
         auto iter = m_wrappers.find(fn);
         if (iter != m_wrappers.end()) {
             freeWrapper(iter->second);