diff --git a/legacyver/item_translator.go b/legacyver/item_translator.go
index a77a880..03aef62 100644
--- a/legacyver/item_translator.go
+++ b/legacyver/item_translator.go
@@ -498,7 +498,7 @@ func (t *DefaultItemTranslator) DowngradeItemPackets(pks []packet.Packet, _ *min
 						panic(itemType)
 					}
 				} else {
-					t.latest.RegisterEntry(entry.Name)
+					t.latest.RegisterEntryRID(entry.Name, int32(entry.RuntimeID))
 					entry.RuntimeID = int16(t.mapping.RegisterEntry(entry.Name))
 				}
 				pk.Items[i] = entry
@@ -717,7 +717,7 @@ func (t *DefaultItemTranslator) UpgradeItemPackets(pks []packet.Packet, _ *minec
 						panic(itemType)
 					}
 				} else {
-					t.latest.RegisterEntry(entry.Name)
+					t.latest.RegisterEntryRID(entry.Name, int32(entry.RuntimeID))
 					entry.RuntimeID = int16(t.mapping.RegisterEntry(entry.Name))
 				}
 				pk.Items[i] = entry
diff --git a/mapping/item.go b/mapping/item.go
index e3babde..4ec7d86 100644
--- a/mapping/item.go
+++ b/mapping/item.go
@@ -12,6 +12,7 @@ type Item interface {
 	// ItemNameToRuntimeID converts a string ID to an item runtime ID.
 	ItemNameToRuntimeID(string) (int32, bool)
 	RegisterEntry(string) int32
+	RegisterEntryRID(string, int32)
 	Air() int32
 	ItemVersion() uint16
 }
@@ -96,6 +97,15 @@ func (m *DefaultItemMapping) RegisterEntry(name string) int32 {
 	return nextRID
 }
 
+func (m *DefaultItemMapping) RegisterEntryRID(name string, rid int32) {
+	defer m.mu.Unlock()
+	m.mu.Lock()
+	if _, ok := m.itemNamesToRuntimeIDs[name]; !ok {
+		m.itemNamesToRuntimeIDs[name] = rid
+		m.itemRuntimeIDsToNames[rid] = name
+	}
+}
+
 func (m *DefaultItemMapping) Air() int32 {
 	defer m.mu.Unlock()
 	m.mu.Lock()