diff --git a/src/EFCore/ChangeTracking/Internal/InternalEntryBase.InternalComplexCollectionEntry.cs b/src/EFCore/ChangeTracking/Internal/InternalEntryBase.InternalComplexCollectionEntry.cs
index d4c7996b72e..f4d7d0dc5a1 100644
--- a/src/EFCore/ChangeTracking/Internal/InternalEntryBase.InternalComplexCollectionEntry.cs
+++ b/src/EFCore/ChangeTracking/Internal/InternalEntryBase.InternalComplexCollectionEntry.cs
@@ -21,6 +21,9 @@ public partial class InternalEntryBase
     internal static readonly bool UseOldBehavior38299 =
         AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore.Issue38299", out var enabled) && enabled;
 
+    internal static readonly bool UseOldBehavior39073 =
+        AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore.Issue39073", out var enabled) && enabled;
+
     private struct InternalComplexCollectionEntry(InternalEntryBase entry, IComplexProperty complexCollection)
     {
         private static readonly bool UseOldBehavior37585 =
@@ -46,7 +49,8 @@ private struct InternalComplexCollectionEntry(InternalEntryBase entry, IComplexP
                 && (defaultState != EntityState.Deleted || original)
                 && (defaultState != EntityState.Added || !original))
             {
-                for (var i = 0; i < entries.Count; i++)
+                var count = UseOldBehavior39073 ? entries.Count : collection.Count;
+                for (var i = 0; i < count; i++)
                 {
                     if (entries[i] != null)
                     {
@@ -151,7 +155,7 @@ private struct InternalComplexCollectionEntry(InternalEntryBase entry, IComplexP
             return _entries;
         }
 
-        private IList? GetCollection(bool original)
+        public IList? GetCollection(bool original)
         {
             if (!UseOldBehavior37585
                 && _containingEntry is InternalComplexEntry complexEntry)
@@ -405,14 +409,20 @@ public void SetState(EntityState oldState, EntityState newState, bool acceptChan
                 setOriginalState = true;
             }
 
-            EnsureCapacity(GetCollection(original: true)?.Count ?? 0, original: true, trim: false);
-            EnsureCapacity(GetCollection(original: false)?.Count ?? 0, original: false, trim: false);
+            var originalCollectionCount = GetCollection(original: true)?.Count ?? 0;
+            var currentCollectionCount = GetCollection(original: false)?.Count ?? 0;
+            EnsureCapacity(originalCollectionCount, original: true, trim: false);
+            EnsureCapacity(currentCollectionCount, original: false, trim: false);
 
             var defaultState = newState == EntityState.Modified && !modifyProperties
                 ? EntityState.Unchanged
                 : newState;
-            var originalEntries = GetOrCreateEntries(original: true, defaultState).ToArray();
-            var currentEntries = GetOrCreateEntries(original: false, defaultState).ToArray();
+            var originalEntries = GetOrCreateEntries(original: true, defaultState)
+                .Take(UseOldBehavior39073 ? int.MaxValue : originalCollectionCount)
+                .ToArray();
+            var currentEntries = GetOrCreateEntries(original: false, defaultState)
+                .Take(UseOldBehavior39073 ? int.MaxValue : currentCollectionCount)
+                .ToArray();
             if (setOriginalState)
             {
                 foreach (var originalEntry in originalEntries)
diff --git a/src/EFCore/ChangeTracking/Internal/InternalEntryBase.cs b/src/EFCore/ChangeTracking/Internal/InternalEntryBase.cs
index bfaed78bae7..6d64cef0c6e 100644
--- a/src/EFCore/ChangeTracking/Internal/InternalEntryBase.cs
+++ b/src/EFCore/ChangeTracking/Internal/InternalEntryBase.cs
@@ -1165,7 +1165,11 @@ public InternalComplexEntry GetComplexCollectionOriginalEntry(IComplexProperty p
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
     public IEnumerable<InternalComplexEntry> GetFlattenedComplexEntries()
-        => _complexCollectionEntries.SelectMany(c => c.GetOrCreateEntries(original: false)).Where(e => e != null)!;
+        => _complexCollectionEntries
+            .SelectMany(
+                c => c.GetOrCreateEntries(original: false)
+                    .Take(UseOldBehavior39073 ? int.MaxValue : c.GetCollection(original: false)?.Count ?? 0))
+            .Where(e => e != null)!;
 
     /// <summary>
     ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
diff --git a/test/EFCore.Tests/ChangeTracking/Internal/InternalComplexEntryTest.cs b/test/EFCore.Tests/ChangeTracking/Internal/InternalComplexEntryTest.cs
index 384f6c72abd..9e45f154efd 100644
--- a/test/EFCore.Tests/ChangeTracking/Internal/InternalComplexEntryTest.cs
+++ b/test/EFCore.Tests/ChangeTracking/Internal/InternalComplexEntryTest.cs
@@ -767,6 +767,43 @@ public void DetectChanges_detects_changes_in_nested_complex_collections()
         Assert.Equal(EntityState.Added, items[2].State);
     }
 
+    [ConditionalFact]
+    public void Entity_can_be_marked_modified_after_nested_complex_collection_shrinks()
+    {
+        var model = CreateModelWithNestedComplexCollection();
+        var complexProperty = model.FindEntityType(typeof(BlogWithNestedCollection))!
+            .FindComplexProperty(nameof(BlogWithNestedCollection.Items))!;
+        var serviceProvider = InMemoryTestHelpers.Instance.CreateContextServices(model);
+        var stateManager = serviceProvider.GetRequiredService<IStateManager>();
+        var changeDetector = serviceProvider.GetRequiredService<IChangeDetector>();
+
+        var blog = new BlogWithNestedCollection
+        {
+            Items =
+            [
+                new NestedCollectionItem { Name = "foo" },
+                new NestedCollectionItem
+                {
+                    Name = "bar",
+                    NestedItems = [new NestedItem { Name = "baz" }]
+                }
+            ]
+        };
+
+        var entityEntry = stateManager.GetOrCreateEntry(blog);
+        entityEntry.SetEntityState(EntityState.Unchanged);
+
+        blog.Items = [new NestedCollectionItem { Name = "foo" }];
+
+        entityEntry.SetEntityState(EntityState.Modified);
+
+        Assert.Equal(EntityState.Modified, entityEntry.EntityState);
+
+        changeDetector.DetectChanges(stateManager);
+
+        Assert.Equal(EntityState.Deleted, entityEntry.GetComplexCollectionOriginalEntry(complexProperty, 1).EntityState);
+    }
+
     private static IModel CreateModel()
     {
         var modelBuilder = InMemoryTestHelpers.Instance.CreateConventionBuilder();
@@ -781,6 +818,18 @@ private static IModel CreateModel()
         return modelBuilder.FinalizeModel();
     }
 
+    private static IModel CreateModelWithNestedComplexCollection()
+    {
+        var modelBuilder = InMemoryTestHelpers.Instance.CreateConventionBuilder();
+
+        modelBuilder.Entity<BlogWithNestedCollection>(
+            b => b.ComplexCollection(
+                e => e.Items,
+                b => b.ComplexCollection(e => e.NestedItems)));
+
+        return modelBuilder.FinalizeModel();
+    }
+
     private static IModel CreateModelWithNestedComplexCollections()
     {
         var modelBuilder = InMemoryTestHelpers.Instance.CreateConventionBuilder();
@@ -831,6 +880,18 @@ private class BlogWithNested
         public NestedJson NestedJson { get; set; } = new();
     }
 
+    private class BlogWithNestedCollection
+    {
+        public int Id { get; set; }
+        public List<NestedCollectionItem> Items { get; set; } = [];
+    }
+
+    private class NestedCollectionItem
+    {
+        public string Name { get; set; } = "";
+        public List<NestedItem> NestedItems { get; set; } = [];
+    }
+
     private record NestedJson
     {
         public NestedItem Item { get; init; } = new();