diff --git a/lib/screens/garage_screen.dart b/lib/screens/garage_screen.dart
index 0a0e52e..df9d5d0 100644
--- a/lib/screens/garage_screen.dart
+++ b/lib/screens/garage_screen.dart
@@ -476,11 +476,12 @@ class GarageScreenState extends State<GarageScreen> {
       );
 
       if (confirmed != true || targetId == null) return;
+      final targetCollectionId = targetId!;
 
       if (isOwner) {
         await supabase
             .from('hotwheels')
-            .update({'collection_id': targetId})
+        .update({'collection_id': targetCollectionId})
             .inFilter('id', _selectedIds.toList());
       } else {
         final userId = supabase.auth.currentUser?.id;
@@ -492,22 +493,54 @@ class GarageScreenState extends State<GarageScreen> {
             .where((car) => _selectedIds.contains(car['id'] as int))
             .toList(growable: false);
 
+        final hwIds = sourceCars
+            .map((car) => car['hw_id'] as String)
+            .toSet()
+            .toList(growable: false);
+
+        final existing = await supabase
+            .from('hotwheels')
+            .select('hw_id')
+          .eq('collection_id', targetCollectionId)
+            .inFilter('hw_id', hwIds);
+        final existingHwIds = (existing as List)
+            .map((row) => row['hw_id'] as String)
+            .toSet();
+
         final insertRows = sourceCars.map((car) {
           final notes = car['notes'] as String?;
           final imagePath = car['user_image_url'] as String?;
           return <String, dynamic>{
             'hw_id': car['hw_id'] as String,
             'user_id': userId,
-            'collection_id': targetId,
+            'collection_id': targetCollectionId,
             if (notes != null && notes.trim().isNotEmpty) 'notes': notes,
             if (imagePath != null && imagePath.isNotEmpty)
               'user_image_url': imagePath,
           };
-        }).toList(growable: false);
+        }).where((row) => !existingHwIds.contains(row['hw_id'] as String)).toList(
+              growable: false,
+            );
+
+        final skippedDuplicates = sourceCars.length - insertRows.length;
+
+        if (insertRows.isEmpty) {
+          showGlobalSnackBar(
+            'All selected cars are already in the target collection.',
+            isError: true,
+          );
+          return;
+        }
 
         if (insertRows.isNotEmpty) {
           await supabase.from('hotwheels').insert(insertRows);
         }
+
+        if (skippedDuplicates > 0) {
+          showGlobalSnackBar(
+            '$skippedDuplicates car(s) skipped because they already exist in target collection.',
+          );
+        }
       }
 
       if (!mounted) return;
@@ -1069,6 +1102,21 @@ class GarageScreenState extends State<GarageScreen> {
           throw Exception('You must be signed in to copy cars.');
         }
 
+        final existing = await supabase
+            .from('hotwheels')
+            .select('id')
+            .eq('collection_id', targetId)
+            .eq('hw_id', car['hw_id'])
+            .maybeSingle();
+
+        if (existing != null) {
+          showGlobalSnackBar(
+            '${car['hw_id']} is already in the target collection.',
+            isError: true,
+          );
+          return;
+        }
+
         final notes = car['notes'] as String?;
         final imagePath = car['user_image_url'] as String?;
         await supabase.from('hotwheels').insert({
diff --git a/lib/services/collection_service.dart b/lib/services/collection_service.dart
index f2fee28..023a52d 100644
--- a/lib/services/collection_service.dart
+++ b/lib/services/collection_service.dart
@@ -114,14 +114,29 @@ class CollectionService {
     final itemCounts = await getCollectionItemCounts(collectionIdList);
 
     final memberCounts = <String, int>{};
-    final members = await supabase
-        .from('collection_members')
-        .select('collection_id')
-        .inFilter('collection_id', collectionIdList);
+    await Future.wait(collectionIdList.map((collectionId) async {
+      try {
+        final rows = await supabase.rpc('get_collection_members', params: {
+          'p_collection_id': collectionId,
+        });
+        memberCounts[collectionId] = (rows as List).length;
+      } catch (_) {
+      }
+    }));
 
-    for (final member in members) {
-      final collectionId = member['collection_id'] as String;
-      memberCounts[collectionId] = (memberCounts[collectionId] ?? 0) + 1;
+    final unresolvedIds = collectionIdList
+        .where((id) => !memberCounts.containsKey(id))
+        .toList(growable: false);
+    if (unresolvedIds.isNotEmpty) {
+      final members = await supabase
+          .from('collection_members')
+          .select('id, collection_id')
+          .inFilter('collection_id', unresolvedIds);
+
+      for (final member in members) {
+        final collectionId = member['collection_id'] as String;
+        memberCounts[collectionId] = (memberCounts[collectionId] ?? 0) + 1;
+      }
     }
 
     final collections = <Collection>[];