diff --git a/src/EFCore/ChangeTracking/Internal/NavigationFixer.cs b/src/EFCore/ChangeTracking/Internal/NavigationFixer.cs
index 7e1ce3bb812..1b811c1d0b3 100644
--- a/src/EFCore/ChangeTracking/Internal/NavigationFixer.cs
+++ b/src/EFCore/ChangeTracking/Internal/NavigationFixer.cs
@@ -587,11 +587,17 @@ private void InitialFixup(
                     var principalEntry = stateManager.FindPrincipal(entry, foreignKey);
                     if (principalEntry != null)
                     {
-                        // Set navigation to principal based on FK properties
-                        SetNavigation(entry, foreignKey.DependentToPrincipal, principalEntry);
+                        var navigation = foreignKey.DependentToPrincipal;
+                        var existingPrincipal = navigation == null ? null : entry[navigation];
+                        if (existingPrincipal == null
+                            || existingPrincipal == principalEntry.Entity)
+                        {
+                            // Set navigation to principal based on FK properties
+                            SetNavigation(entry, navigation, principalEntry);
 
-                        // Add this entity to principal's collection, or set inverse for 1:1
-                        ToDependentFixup(entry, principalEntry, foreignKey);
+                            // Add this entity to principal's collection, or set inverse for 1:1
+                            ToDependentFixup(entry, principalEntry, foreignKey);
+                        }
                     }
                 }
             }
diff --git a/test/EFCore.Tests/ChangeTracking/Internal/FixupTest.cs b/test/EFCore.Tests/ChangeTracking/Internal/FixupTest.cs
index a546703977b..2d74331e2f2 100644
--- a/test/EFCore.Tests/ChangeTracking/Internal/FixupTest.cs
+++ b/test/EFCore.Tests/ChangeTracking/Internal/FixupTest.cs
@@ -4,8 +4,11 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
 using System.Linq;
+using Microsoft.EntityFrameworkCore.Diagnostics;
 using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Metadata.Internal;
 using Microsoft.EntityFrameworkCore.Storage;
 using Xunit;
 
@@ -2750,6 +2753,64 @@ protected internal override void OnConfiguring(DbContextOptionsBuilder optionsBu
             public DbSet<Level2> Level2s { get; set; }
         }
 
+        [ConditionalFact]
+        public void Detached_entity_is_not_replaced_by_tracked_entity()
+        {
+            using (var context = new BadBeeContext(nameof(BadBeeContext)))
+            {
+                var b1 = new EntityB
+                {
+                    EntityBId = 1
+                };
+                context.BEntities.Attach(b1);
+
+                var b2 = new EntityB
+                {
+                    EntityBId = 1
+                };
+
+                var a = new EntityA
+                {
+                    EntityAId = 1, EntityB = b2
+                };
+
+                Assert.Equal(
+                    CoreStrings.IdentityConflict(
+                        nameof(EntityB),
+                        $"{{'{nameof(EntityB.EntityBId)}'}}"),
+                    Assert.Throws<InvalidOperationException>(() => context.Add(a)).Message);
+            }
+        }
+
+        private class EntityB
+        {
+            public int EntityBId { get; set; }
+            public EntityA EntityA { get; set; }
+        }
+
+        private class EntityA
+        {
+            public int EntityAId { get; set; }
+            public int? EntityBId { get; set; }
+            public EntityB EntityB { get; set; }
+        }
+
+        private class BadBeeContext : DbContext
+        {
+            private readonly string _databaseName;
+
+            public BadBeeContext(string databaseName)
+            {
+                _databaseName = databaseName;
+            }
+
+            protected internal override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
+                => optionsBuilder.UseInMemoryDatabase(_databaseName);
+
+            public DbSet<EntityA> AEntities { get; set; }
+            public DbSet<EntityB> BEntities { get; set; }
+        }
+
         protected virtual void AssertAllFixedUp(DbContext context)
         {
             foreach (var entry in context.ChangeTracker.Entries<Product>())
diff --git a/test/EFCore.Tests/DbContextTrackingTest.cs b/test/EFCore.Tests/DbContextTrackingTest.cs
index fe7446a2006..9777b926834 100644
--- a/test/EFCore.Tests/DbContextTrackingTest.cs
+++ b/test/EFCore.Tests/DbContextTrackingTest.cs
@@ -1498,6 +1498,7 @@ public void Can_attach_with_inconsistent_FK_dependent_first_fully_fixed_up_with_
                     Id = 1,
                     Name = "Beverages"
                 };
+
                 var product = new Product
                 {
                     Id = 1,
@@ -1505,6 +1506,7 @@ public void Can_attach_with_inconsistent_FK_dependent_first_fully_fixed_up_with_
                     Name = "Marmite",
                     Category = category
                 };
+
                 category.Products = new List<Product>
                 {
                     product
@@ -1512,11 +1514,12 @@ public void Can_attach_with_inconsistent_FK_dependent_first_fully_fixed_up_with_
 
                 context.Attach(product);
 
-                Assert.Equal(7, product.CategoryId);
+                Assert.Equal(1, product.CategoryId);
                 Assert.Same(product, category.Products.Single());
-                Assert.Same(category7, product.Category);
-                Assert.Same(product, category7.Products.Single());
-                Assert.Equal(EntityState.Detached, context.Entry(category).State);
+                Assert.Same(category, product.Category);
+                Assert.Empty(category7.Products);
+                Assert.Equal(EntityState.Unchanged, context.Entry(category7).State);
+                Assert.Equal(EntityState.Unchanged, context.Entry(category).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(product).State);
 
                 context.Attach(category);
@@ -1524,6 +1527,8 @@ public void Can_attach_with_inconsistent_FK_dependent_first_fully_fixed_up_with_
                 Assert.Equal(1, product.CategoryId);
                 Assert.Same(product, category.Products.Single());
                 Assert.Same(category, product.Category);
+                Assert.Empty(category7.Products);
+                Assert.Equal(EntityState.Unchanged, context.Entry(category7).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(category).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(product).State);
             }
@@ -1546,6 +1551,7 @@ public void Can_attach_with_inconsistent_FK_principal_first_collection_not_fixed
                     Id = 1,
                     Name = "Beverages"
                 };
+
                 var product = new Product
                 {
                     Id = 1,
@@ -1553,6 +1559,7 @@ public void Can_attach_with_inconsistent_FK_principal_first_collection_not_fixed
                     Name = "Marmite",
                     Category = category
                 };
+
                 category.Products = new List<Product>();
 
                 context.Attach(category);
@@ -1560,16 +1567,18 @@ public void Can_attach_with_inconsistent_FK_principal_first_collection_not_fixed
                 Assert.Equal(7, product.CategoryId);
                 Assert.Empty(category.Products);
                 Assert.Same(category, product.Category);
-                Assert.Empty(category7.Products);
+                Assert.Empty(category.Products);
+                Assert.Equal(EntityState.Unchanged, context.Entry(category7).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(category).State);
                 Assert.Equal(EntityState.Detached, context.Entry(product).State);
 
                 context.Attach(product);
 
-                Assert.Equal(7, product.CategoryId);
-                Assert.Empty(category.Products);
-                Assert.Same(category7, product.Category);
-                Assert.Same(product, category7.Products.Single());
+                Assert.Equal(1, product.CategoryId);
+                Assert.Same(product, category.Products.Single());
+                Assert.Same(category, product.Category);
+                Assert.Empty(category7.Products);
+                Assert.Equal(EntityState.Unchanged, context.Entry(category7).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(category).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(product).State);
             }
@@ -1592,6 +1601,7 @@ public void Can_attach_with_inconsistent_FK_dependent_first_collection_not_fixed
                     Id = 1,
                     Name = "Beverages"
                 };
+
                 var product = new Product
                 {
                     Id = 1,
@@ -1599,23 +1609,26 @@ public void Can_attach_with_inconsistent_FK_dependent_first_collection_not_fixed
                     Name = "Marmite",
                     Category = category
                 };
+
                 category.Products = new List<Product>();
 
                 context.Attach(product);
 
-                Assert.Equal(7, product.CategoryId);
-                Assert.Empty(category.Products);
-                Assert.Same(category7, product.Category);
-                Assert.Same(product, category7.Products.Single());
-                Assert.Equal(EntityState.Detached, context.Entry(category).State);
+                Assert.Equal(1, product.CategoryId);
+                Assert.Same(product, category.Products.Single());
+                Assert.Same(category, product.Category);
+                Assert.Empty(category7.Products);
+                Assert.Equal(EntityState.Unchanged, context.Entry(category7).State);
+                Assert.Equal(EntityState.Unchanged, context.Entry(category).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(product).State);
 
                 context.Attach(category);
 
-                Assert.Equal(7, product.CategoryId);
-                Assert.Empty(category.Products);
-                Assert.Same(category7, product.Category);
-                Assert.Same(product, category7.Products.Single());
+                Assert.Equal(1, product.CategoryId);
+                Assert.Same(product, category.Products.Single());
+                Assert.Same(category, product.Category);
+                Assert.Empty(category7.Products);
+                Assert.Equal(EntityState.Unchanged, context.Entry(category7).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(category).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(product).State);
             }
@@ -1782,6 +1795,7 @@ public void Can_set_set_to_Unchanged_with_inconsistent_FK_dependent_first_fully_
                     Id = 1,
                     Name = "Beverages"
                 };
+
                 var product = new Product
                 {
                     Id = 1,
@@ -1789,6 +1803,7 @@ public void Can_set_set_to_Unchanged_with_inconsistent_FK_dependent_first_fully_
                     Name = "Marmite",
                     Category = category
                 };
+
                 category.Products = new List<Product>
                 {
                     product
@@ -1798,8 +1813,9 @@ public void Can_set_set_to_Unchanged_with_inconsistent_FK_dependent_first_fully_
 
                 Assert.Equal(7, product.CategoryId);
                 Assert.Same(product, category.Products.Single());
-                Assert.Same(category7, product.Category);
-                Assert.Same(product, category7.Products.Single());
+                Assert.Same(category, product.Category);
+                Assert.Empty(category7.Products);
+                Assert.Equal(EntityState.Unchanged, context.Entry(category7).State);
                 Assert.Equal(EntityState.Detached, context.Entry(category).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(product).State);
 
@@ -1808,6 +1824,8 @@ public void Can_set_set_to_Unchanged_with_inconsistent_FK_dependent_first_fully_
                 Assert.Equal(1, product.CategoryId);
                 Assert.Same(product, category.Products.Single());
                 Assert.Same(category, product.Category);
+                Assert.Empty(category7.Products);
+                Assert.Equal(EntityState.Unchanged, context.Entry(category7).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(category).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(product).State);
             }
@@ -1850,10 +1868,11 @@ public void Can_set_set_to_Unchanged_with_inconsistent_FK_principal_first_collec
 
                 context.Entry(product).State = EntityState.Unchanged;
 
-                Assert.Equal(7, product.CategoryId);
-                Assert.Empty(category.Products);
-                Assert.Same(category7, product.Category);
-                Assert.Same(product, category7.Products.Single());
+                Assert.Equal(1, product.CategoryId);
+                Assert.Same(product, category.Products.Single());
+                Assert.Same(category, product.Category);
+                Assert.Empty(category7.Products);
+                Assert.Equal(EntityState.Unchanged, context.Entry(category7).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(category).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(product).State);
             }
@@ -1876,6 +1895,7 @@ public void Can_set_set_to_Unchanged_with_inconsistent_FK_dependent_first_collec
                     Id = 1,
                     Name = "Beverages"
                 };
+
                 var product = new Product
                 {
                     Id = 1,
@@ -1883,23 +1903,26 @@ public void Can_set_set_to_Unchanged_with_inconsistent_FK_dependent_first_collec
                     Name = "Marmite",
                     Category = category
                 };
+
                 category.Products = new List<Product>();
 
                 context.Entry(product).State = EntityState.Unchanged;
 
                 Assert.Equal(7, product.CategoryId);
                 Assert.Empty(category.Products);
-                Assert.Same(category7, product.Category);
-                Assert.Same(product, category7.Products.Single());
+                Assert.Same(category, product.Category);
+                Assert.Empty(category7.Products);
                 Assert.Equal(EntityState.Detached, context.Entry(category).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(product).State);
+                Assert.Equal(EntityState.Unchanged, context.Entry(category7).State);
 
                 context.Entry(category).State = EntityState.Unchanged;
 
-                Assert.Equal(7, product.CategoryId);
-                Assert.Empty(category.Products);
-                Assert.Same(category7, product.Category);
-                Assert.Same(product, category7.Products.Single());
+                Assert.Equal(1, product.CategoryId);
+                Assert.Same(product, category.Products.Single());
+                Assert.Same(category, product.Category);
+                Assert.Empty(category7.Products);
+                Assert.Equal(EntityState.Unchanged, context.Entry(category7).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(category).State);
                 Assert.Equal(EntityState.Unchanged, context.Entry(product).State);
             }