diff --git a/src/p_acs.cpp b/src/p_acs.cpp
index 9fee64925..d8e45ba1a 100644
--- a/src/p_acs.cpp
+++ b/src/p_acs.cpp
@@ -406,28 +406,54 @@ void P_WriteACSVars(FILE *stdfile)
 
 static void DoClearInv (AActor *actor)
 {
-	AInventory *inv = actor->Inventory;
+	// In case destroying an inventory item causes another to be destroyed
+	// (e.g. Weapons destroy their sisters), keep track of the pointer to
+	// the next inventory item rather than the next inventory item itself.
+	// For example, if a weapon is immediately followed by its sister, the
+	// next weapon we had tracked would be to the sister, so it is now
+	// invalid and we won't be able to find the complete inventory by
+	// following it.
+	//
+	// When we destroy an item, we leave invp alone, since the destruction
+	// process will leave it pointing to the next item we want to check. If
+	// we don't destroy an item, then we move invp to point to its Inventory
+	// pointer.
+	//
+	// It should be safe to assume that an item being destroyed will only
+	// destroy items further down in the chain, because if it was going to
+	// destroy something we already processed, we've already destroyed it,
+	// so it won't have anything to destroy.
 
-	while (inv != NULL)
+	AInventory **invp = &actor->Inventory;
+
+	while (*invp != NULL)
 	{
-		AInventory *next = inv->Inventory;
+		AInventory *inv = *invp;
 		if (!(inv->ItemFlags & IF_UNDROPPABLE))
 		{
-			// Fix for undroppable weapons. Is this ok?
+			// For the sake of undroppable weapons, never remove ammo once
+			// it has been acquired; just set its amount to 0.
 			if (inv->IsKindOf(RUNTIME_CLASS(AAmmo)))
 			{
 				AAmmo *ammo = static_cast<AAmmo*>(inv);
 				ammo->Amount = 0;
+				invp = &inv->Inventory;
 			}
 			else
+			{
 				inv->Destroy ();
+			}
 		}
 		else if (inv->GetClass() == RUNTIME_CLASS(AHexenArmor))
 		{
 			AHexenArmor *harmor = static_cast<AHexenArmor *> (inv);
 			harmor->Slots[3] = harmor->Slots[2] = harmor->Slots[1] = harmor->Slots[0] = 0;
+			invp = &inv->Inventory;
+		}
+		else
+		{
+			invp = &inv->Inventory;
 		}
-		inv = next;
 	}
 	if (actor->player != NULL)
 	{