diff --git a/source/CardManager.cpp b/source/CardManager.cpp
index d71e31b1..2cb25465 100644
--- a/source/CardManager.cpp
+++ b/source/CardManager.cpp
@@ -120,6 +120,12 @@ void CardManager::RemoveInternal(UINT slot)
 	m_slot[slot] = NULL;
 }
 
+void CardManager::RemoveAuxInternal()
+{
+	delete m_aux;
+	m_aux = NULL;
+}
+
 void CardManager::Remove(UINT slot)
 {
 	RemoveInternal(slot);
@@ -131,6 +137,8 @@ void CardManager::InsertAux(SS_CARDTYPE type)
 	if (type == CT_Empty)
 		return RemoveAux();
 
+	RemoveAuxInternal();
+
 	switch (type)
 	{
 	case CT_80Col:
@@ -146,10 +154,13 @@ void CardManager::InsertAux(SS_CARDTYPE type)
 		_ASSERT(0);
 		break;
 	}
+
+	// for consistency m_aux must never be NULL
+	_ASSERT(m_aux != NULL);
 }
 
 void CardManager::RemoveAux(void)
 {
-	delete m_aux;
+	RemoveAuxInternal();
 	m_aux = new EmptyCard;
 }
diff --git a/source/CardManager.h b/source/CardManager.h
index d7807d1d..367cafae 100644
--- a/source/CardManager.h
+++ b/source/CardManager.h
@@ -24,8 +24,8 @@ public:
 	~CardManager(void)
 	{
 		for (UINT i=0; i<NUM_SLOTS; i++)
-			Remove(i);
-		RemoveAux();
+			RemoveInternal(i);
+		RemoveAuxInternal();
 	}
 
 	void Insert(UINT slot, SS_CARDTYPE type);
@@ -34,7 +34,6 @@ public:
 	Card& GetRef(UINT slot)
 	{
 		SS_CARDTYPE t=QuerySlot(slot); _ASSERT((t==CT_SSC || t==CT_MouseInterface || t==CT_Disk2) && m_slot[slot]);
-		if (!m_slot[slot]) throw std::runtime_error("slot/card mismatch");
 		return *m_slot[slot];
 	}
 	Card* GetObj(UINT slot) { SS_CARDTYPE t=QuerySlot(slot); _ASSERT(t==CT_SSC || t==CT_MouseInterface || t==CT_Disk2); return m_slot[slot]; }
@@ -54,6 +53,7 @@ public:
 
 private:
 	void RemoveInternal(UINT slot);
+	void RemoveAuxInternal();
 
 	Card* m_slot[NUM_SLOTS];
 	Card* m_aux;