diff --git a/uppsrc/Core/Index.h b/uppsrc/Core/Index.h
index 4fb6dace4..b77a83697 100644
--- a/uppsrc/Core/Index.h
+++ b/uppsrc/Core/Index.h
@@ -164,6 +164,7 @@ public:
 
 	V        PickKeys() pick_                 { return key; }
 	const V& GetKeys() const                  { return key; }
+	bool     IsPicked(void) const             { return key.IsPicked(); }
 
 // Pick assignment & copy. Picked source can only Clear(), ~AIndex(), operator=, operator<<=
 
diff --git a/uppsrc/Core/Vcont.cpp b/uppsrc/Core/Vcont.cpp
index 9fc228e2d..cd67aa67b 100644
--- a/uppsrc/Core/Vcont.cpp
+++ b/uppsrc/Core/Vcont.cpp
@@ -8,6 +8,23 @@ struct Vector_ {
 	int   alloc;
 };
 
+#ifdef _DEBUG
+
+void *break_when_picked;
+
+void BreakWhenPicked(void *ptr)
+{
+	if(ptr == break_when_picked)
+		__BREAK__;
+}
+
+void BREAK_WHEN_PICKED__(void *ptr)
+{
+	break_when_picked = ptr;
+}
+
+#endif
+
 void VectorReAlloc_(void *v_, int newalloc, int sizeofT)
 {
 	Vector_ *v = (Vector_*)v_;
diff --git a/uppsrc/Core/Vcont.h b/uppsrc/Core/Vcont.h
index 7a09d2f6e..23b17ac44 100644
--- a/uppsrc/Core/Vcont.h
+++ b/uppsrc/Core/Vcont.h
@@ -1,3 +1,14 @@
+#ifdef _DEBUG
+void BreakWhenPicked(void *ptr);
+void BREAK_WHEN_PICKED__(void *ptr);
+
+template <class T>
+void BREAK_WHEN_PICKED(T& x)
+{
+	BREAK_WHEN_PICKED__(&x);
+}
+#endif
+
 template <class T>
 class Vector : public MoveableAndDeepCopyOption< Vector<T> > {
 	T       *vector;
@@ -6,7 +17,12 @@ class Vector : public MoveableAndDeepCopyOption< Vector<T> > {
 
 	static void    RawFree(T *ptr)            { if(ptr) MemoryFree(ptr); }
 	static T      *RawAlloc(int& n);
+
+#ifdef _DEBUG
+	static Vector& SetPicked(pick_ Vector& v) { BreakWhenPicked(&v); Vector& p = (Vector&)(v); p.items = -1; p.vector = NULL; return p; }
+#else
 	static Vector& SetPicked(pick_ Vector& v) { Vector& p = (Vector&)(v); p.items = -1; p.vector = NULL; return p; }
+#endif
 
 	void     Pick(pick_ Vector<T>& v);