diff --git a/src/Umbraco.Core/Persistence/Migrations/MigrationExpressionBase.cs b/src/Umbraco.Core/Persistence/Migrations/MigrationExpressionBase.cs
index 3b8b62258e..fc7b4f3b58 100644
--- a/src/Umbraco.Core/Persistence/Migrations/MigrationExpressionBase.cs
+++ b/src/Umbraco.Core/Persistence/Migrations/MigrationExpressionBase.cs
@@ -29,5 +29,11 @@ namespace Umbraco.Core.Persistence.Migrations
         {
             return this.ToString();
         }
+
+        /// <summary>
+        /// This might be useful in the future if we add it to the interface, but for now it's used to hack the DeleteAppTables & DeleteForeignKeyExpression
+        /// to ensure they are not executed twice.
+        /// </summary>
+        internal string Name { get; set; }
     }
 }
\ No newline at end of file
diff --git a/src/Umbraco.Core/Persistence/Migrations/Upgrades/TargetVersionFourNineZero/RemoveUmbracoAppConstraints.cs b/src/Umbraco.Core/Persistence/Migrations/Upgrades/TargetVersionFourNineZero/RemoveUmbracoAppConstraints.cs
index 9ecb530578..eac7ef7c9a 100644
--- a/src/Umbraco.Core/Persistence/Migrations/Upgrades/TargetVersionFourNineZero/RemoveUmbracoAppConstraints.cs
+++ b/src/Umbraco.Core/Persistence/Migrations/Upgrades/TargetVersionFourNineZero/RemoveUmbracoAppConstraints.cs
@@ -25,7 +25,9 @@ namespace Umbraco.Core.Persistence.Migrations.Upgrades.TargetVersionFourNineZero
 
                 if (constraints.Any(x => x.Item1.InvariantEquals("umbracoUser2app") && x.Item3.InvariantEquals("FK_umbracoUser2app_umbracoApp")))
                 {
-                    Delete.ForeignKey("FK_umbracoUser2app_umbracoApp").OnTable("umbracoUser2app");    
+                    Delete.ForeignKey("FK_umbracoUser2app_umbracoApp").OnTable("umbracoUser2app");
+                    //name this migration, this is a hack for DeleteAppTables to ensure it's not executed twice
+                    ((MigrationExpressionBase) Context.Expressions.Last()).Name = "FK_umbracoUser2app_umbracoApp";
                 }
                 if (constraints.Any(x => x.Item1.InvariantEquals("umbracoUser2app") && x.Item3.InvariantEquals("FK_umbracoUser2app_umbracoUser")))
                 {
diff --git a/src/Umbraco.Core/Persistence/Migrations/Upgrades/TargetVersionSix/DeleteAppTables.cs b/src/Umbraco.Core/Persistence/Migrations/Upgrades/TargetVersionSix/DeleteAppTables.cs
index 05edf00062..2b5f65e716 100644
--- a/src/Umbraco.Core/Persistence/Migrations/Upgrades/TargetVersionSix/DeleteAppTables.cs
+++ b/src/Umbraco.Core/Persistence/Migrations/Upgrades/TargetVersionSix/DeleteAppTables.cs
@@ -1,4 +1,6 @@
-using Umbraco.Core.Configuration;
+using System.Linq;
+using Umbraco.Core.Configuration;
+using Umbraco.Core.Persistence.SqlSyntax;
 
 namespace Umbraco.Core.Persistence.Migrations.Upgrades.TargetVersionSix
 {
@@ -10,6 +12,31 @@ namespace Umbraco.Core.Persistence.Migrations.Upgrades.TargetVersionSix
         {
             Delete.Table("umbracoAppTree");
 
+            //NOTE: this is a hack since old umbraco versions might not have had their db's upgraded correctly so they are all quite inconsistent.
+            // This is actually done in migration: RemoveUmbracoAppConstraints to target 4.9.0 but we've found with some db's that are currently at 4.9.1, 
+            // these upgrades did not run. So, now we not only have to check if these constraints exist, but we also have to check if the RemoveUmbracoAppConstraints
+            // has executed since we cannot drop the same foreign key twice or we'll get errors.
+
+            //Here we'll do a dirty check to see if RemoveUmbracoAppConstraints has executed
+            if (Context.Expressions.Any(x =>
+            {
+                var b = x as MigrationExpressionBase;
+                if (b == null) return false;
+                return b.Name == "FK_umbracoUser2app_umbracoApp";
+            }) == false)
+            {
+                //These are the old aliases, before removing them, check they exist
+                var constraints = SqlSyntaxContext.SqlSyntaxProvider.GetConstraintsPerColumn(Context.Database).Distinct().ToArray();
+                if (constraints.Any(x => x.Item1.InvariantEquals("umbracoUser2app") && x.Item3.InvariantEquals("FK_umbracoUser2app_umbracoApp")))
+                {
+                    Delete.ForeignKey("FK_umbracoUser2app_umbracoApp").OnTable("umbracoUser2app");
+                }
+                if (constraints.Any(x => x.Item1.InvariantEquals("umbracoUser2app") && x.Item3.InvariantEquals("FK_umbracoUser2app_umbracoUser")))
+                {
+                    Delete.ForeignKey("FK_umbracoUser2app_umbracoUser").OnTable("umbracoUser2app");
+                }    
+            }
+
             Delete.Table("umbracoApp");
         }