diff --git a/src/Infrastructure.EntityFramework/Repositories/CollectionCipherRepository.cs b/src/Infrastructure.EntityFramework/Repositories/CollectionCipherRepository.cs
index 6e2805f987..39e3ab8019 100644
--- a/src/Infrastructure.EntityFramework/Repositories/CollectionCipherRepository.cs
+++ b/src/Infrastructure.EntityFramework/Repositories/CollectionCipherRepository.cs
@@ -1,4 +1,5 @@
 using AutoMapper;
+using Bit.Core.Enums;
 using Bit.Core.Repositories;
 using Bit.Infrastructure.EntityFramework.Repositories.Queries;
 using Microsoft.EntityFrameworkCore;
@@ -145,9 +146,11 @@ public class CollectionCipherRepository : BaseEntityFrameworkRepository, ICollec
         using (var scope = ServiceScopeFactory.CreateScope())
         {
             var dbContext = GetDatabaseContext(scope);
-            var availableCollections = await (from c in dbContext.Collections
-                                              where c.OrganizationId == organizationId
-                                              select c).ToListAsync();
+
+            var availableCollectionIds = await (from c in dbContext.Collections
+                                                where c.OrganizationId == organizationId
+                                                && c.Type != CollectionType.DefaultUserCollection
+                                                select c.Id).ToListAsync();
 
             var currentCollectionCiphers = await (from cc in dbContext.CollectionCiphers
                                                   where cc.CipherId == cipherId
@@ -155,6 +158,8 @@ public class CollectionCipherRepository : BaseEntityFrameworkRepository, ICollec
 
             foreach (var requestedCollectionId in collectionIds)
             {
+                if (!availableCollectionIds.Contains(requestedCollectionId)) continue;
+
                 var requestedCollectionCipher = currentCollectionCiphers
                     .FirstOrDefault(cc => cc.CollectionId == requestedCollectionId);
 
@@ -168,7 +173,7 @@ public class CollectionCipherRepository : BaseEntityFrameworkRepository, ICollec
                 }
             }
 
-            dbContext.RemoveRange(currentCollectionCiphers.Where(cc => !collectionIds.Contains(cc.CollectionId)));
+            dbContext.RemoveRange(currentCollectionCiphers.Where(cc => availableCollectionIds.Contains(cc.CollectionId) && !collectionIds.Contains(cc.CollectionId)));
             await dbContext.UserBumpAccountRevisionDateByOrganizationIdAsync(organizationId);
             await dbContext.SaveChangesAsync();
         }
diff --git a/src/Sql/dbo/Stored Procedures/CollectionCipher_UpdateCollections.sql b/src/Sql/dbo/Stored Procedures/CollectionCipher_UpdateCollections.sql
index f3a1d964b5..2282524228 100644
--- a/src/Sql/dbo/Stored Procedures/CollectionCipher_UpdateCollections.sql	
+++ b/src/Sql/dbo/Stored Procedures/CollectionCipher_UpdateCollections.sql	
@@ -44,13 +44,13 @@ BEGIN
         [CollectionId],
         [CipherId]
     )
-    SELECT 
+    SELECT
         [Id],
         @CipherId
     FROM @CollectionIds
     WHERE [Id] IN (SELECT [Id] FROM [#TempAvailableCollections])
     AND NOT EXISTS (
-        SELECT 1 
+        SELECT 1
         FROM [dbo].[CollectionCipher]
         WHERE [CollectionId] = [@CollectionIds].[Id]
         AND [CipherId] = @CipherId
diff --git a/src/Sql/dbo/Stored Procedures/CollectionCipher_UpdateCollectionsAdmin.sql b/src/Sql/dbo/Stored Procedures/CollectionCipher_UpdateCollectionsAdmin.sql
index 5f7b0215d9..1486709f09 100644
--- a/src/Sql/dbo/Stored Procedures/CollectionCipher_UpdateCollectionsAdmin.sql	
+++ b/src/Sql/dbo/Stored Procedures/CollectionCipher_UpdateCollectionsAdmin.sql	
@@ -4,46 +4,52 @@
     @CollectionIds AS [dbo].[GuidIdArray] READONLY
 AS
 BEGIN
-    SET NOCOUNT ON
+    SET NOCOUNT ON;
 
-    ;WITH [AvailableCollectionsCTE] AS(
-        SELECT
-            Id
-        FROM
-            [dbo].[Collection]
-        WHERE
-            OrganizationId = @OrganizationId
-    ),
-    [CollectionCiphersCTE] AS(
-        SELECT
-            [CollectionId],
-            [CipherId]
-        FROM
-            [dbo].[CollectionCipher]
-        WHERE
-            [CipherId] = @CipherId
+    -- Available collections for this org, excluding default collections
+    SELECT
+        C.[Id]
+    INTO #TempAvailableCollections
+    FROM [dbo].[Collection] AS C
+    WHERE
+        C.[OrganizationId] = @OrganizationId
+        AND C.[Type] <> 1;  -- exclude DefaultUserCollection
+
+    -- Insert new collection assignments
+    INSERT INTO [dbo].[CollectionCipher] (
+        [CollectionId],
+        [CipherId]
     )
-    MERGE
-        [CollectionCiphersCTE] AS [Target]
-    USING 
-        @CollectionIds AS [Source]
-    ON
-        [Target].[CollectionId] = [Source].[Id]
-        AND [Target].[CipherId] = @CipherId
-    WHEN NOT MATCHED BY TARGET
-    AND [Source].[Id] IN (SELECT [Id] FROM [AvailableCollectionsCTE]) THEN
-        INSERT VALUES
-        (
-            [Source].[Id],
-            @CipherId
-        )
-    WHEN NOT MATCHED BY SOURCE
-    AND [Target].[CipherId] = @CipherId THEN
-        DELETE
-    ;
+    SELECT
+        S.[Id],
+        @CipherId
+    FROM @CollectionIds AS S
+    INNER JOIN #TempAvailableCollections AS A
+        ON A.[Id] = S.[Id]
+    WHERE NOT EXISTS (
+        SELECT 1
+        FROM [dbo].[CollectionCipher] AS CC
+        WHERE CC.[CollectionId] = S.[Id]
+          AND CC.[CipherId]    = @CipherId
+    );
+
+    -- Delete removed collection assignments
+    DELETE CC
+    FROM [dbo].[CollectionCipher] AS CC
+    INNER JOIN #TempAvailableCollections AS A
+        ON A.[Id] = CC.[CollectionId]
+    WHERE CC.[CipherId] = @CipherId
+      AND NOT EXISTS (
+          SELECT 1
+          FROM @CollectionIds AS S
+          WHERE S.[Id] = CC.[CollectionId]
+      );
 
     IF @OrganizationId IS NOT NULL
     BEGIN
-        EXEC [dbo].[User_BumpAccountRevisionDateByOrganizationId] @OrganizationId
+        EXEC [dbo].[User_BumpAccountRevisionDateByOrganizationId] @OrganizationId;
     END
-END
\ No newline at end of file
+
+    DROP TABLE #TempAvailableCollections;
+END
+GO
diff --git a/util/Migrator/DbScripts/2025-09-23_00_UpdateCollectionCipher_UpdateCollectionsAdmin.sql b/util/Migrator/DbScripts/2025-09-23_00_UpdateCollectionCipher_UpdateCollectionsAdmin.sql
new file mode 100644
index 0000000000..f69fdb30ff
--- /dev/null
+++ b/util/Migrator/DbScripts/2025-09-23_00_UpdateCollectionCipher_UpdateCollectionsAdmin.sql
@@ -0,0 +1,55 @@
+CREATE OR ALTER PROCEDURE [dbo].[CollectionCipher_UpdateCollectionsAdmin]
+    @CipherId UNIQUEIDENTIFIER,
+    @OrganizationId UNIQUEIDENTIFIER,
+    @CollectionIds AS [dbo].[GuidIdArray] READONLY
+AS
+BEGIN
+    SET NOCOUNT ON;
+
+    -- Available collections for this org, excluding default collections
+    SELECT
+        C.[Id]
+    INTO #TempAvailableCollections
+    FROM [dbo].[Collection] AS C
+    WHERE
+        C.[OrganizationId] = @OrganizationId
+        AND C.[Type] <> 1;  -- exclude DefaultUserCollection
+
+    -- Insert new collection assignments
+    INSERT INTO [dbo].[CollectionCipher] (
+        [CollectionId],
+        [CipherId]
+    )
+    SELECT
+        S.[Id],
+        @CipherId
+    FROM @CollectionIds AS S
+    INNER JOIN #TempAvailableCollections AS A
+        ON A.[Id] = S.[Id]
+    WHERE NOT EXISTS (
+        SELECT 1
+        FROM [dbo].[CollectionCipher] AS CC
+        WHERE CC.[CollectionId] = S.[Id]
+          AND CC.[CipherId]    = @CipherId
+    );
+
+    -- Delete removed collection assignments
+    DELETE CC
+    FROM [dbo].[CollectionCipher] AS CC
+    INNER JOIN #TempAvailableCollections AS A
+        ON A.[Id] = CC.[CollectionId]
+    WHERE CC.[CipherId] = @CipherId
+      AND NOT EXISTS (
+          SELECT 1
+          FROM @CollectionIds AS S
+          WHERE S.[Id] = CC.[CollectionId]
+      );
+
+    IF @OrganizationId IS NOT NULL
+    BEGIN
+        EXEC [dbo].[User_BumpAccountRevisionDateByOrganizationId] @OrganizationId;
+    END
+
+    DROP TABLE #TempAvailableCollections;
+END
+GO