diff --git a/src/Umbraco.Core/Persistence/NPocoSqlExtensions.cs b/src/Umbraco.Core/Persistence/NPocoSqlExtensions.cs
index 18027bcc1b..7aa8b707be 100644
--- a/src/Umbraco.Core/Persistence/NPocoSqlExtensions.cs
+++ b/src/Umbraco.Core/Persistence/NPocoSqlExtensions.cs
@@ -662,6 +662,26 @@ namespace Umbraco.Core.Persistence
             return sql.Select(sql.GetColumns(columnExpressions: fields));
         }
 
+        /// <summary>
+        /// Creates a SELECT DISTINCT Sql statement.
+        /// </summary>
+        /// <typeparam name="TDto">The type of the DTO to select.</typeparam>
+        /// <param name="sql">The origin sql.</param>
+        /// <param name="fields">Expressions indicating the columns to select.</param>
+        /// <returns>The Sql statement.</returns>
+        /// <remarks>
+        /// <para>If <paramref name="fields"/> is empty, all columns are selected.</para>
+        /// </remarks>
+        public static Sql<ISqlContext> SelectDistinct<TDto>(this Sql<ISqlContext> sql, params Expression<Func<TDto, object>>[] fields)
+        {
+            if (sql == null) throw new ArgumentNullException(nameof(sql));
+            var columns = sql.GetColumns(columnExpressions: fields);
+            sql.Append("SELECT DISTINCT " + string.Join(", ", columns));
+            return sql;
+        }
+
+        //this.Append("SELECT " + string.Join(", ", columns), new object[0]);
+
         /// <summary>
         /// Creates a SELECT Sql statement.
         /// </summary>
diff --git a/src/Umbraco.Core/Persistence/Repositories/Implement/ContentTypeRepositoryBase.cs b/src/Umbraco.Core/Persistence/Repositories/Implement/ContentTypeRepositoryBase.cs
index 055ed7ae74..662254d1ee 100644
--- a/src/Umbraco.Core/Persistence/Repositories/Implement/ContentTypeRepositoryBase.cs
+++ b/src/Umbraco.Core/Persistence/Repositories/Implement/ContentTypeRepositoryBase.cs
@@ -809,7 +809,7 @@ AND umbracoNode.id <> @id",
 
             var targetLanguageIdS = targetLanguageId.HasValue ? targetLanguageId.ToString() : "NULL";
             var sqlSelectTagsToInsert = Sql()
-                .Select<TagDto>(x => x.Text, x => x.Group)
+                .SelectDistinct<TagDto>(x => x.Text, x => x.Group)
                 .Append(", " + targetLanguageIdS)
                 .From<TagDto>();
 
@@ -840,7 +840,7 @@ AND umbracoNode.id <> @id",
             // and group, but for the target language
 
             var sqlSelectRelationsToInsert = Sql()
-                .Select<TagRelationshipDto>(x => x.NodeId, x => x.PropertyTypeId)
+                .SelectDistinct<TagRelationshipDto>(x => x.NodeId, x => x.PropertyTypeId)
                 .AndSelect<TagDto>("otag", x => x.Id)
                 .From<TagRelationshipDto>()
                 .InnerJoin<TagDto>().On<TagRelationshipDto, TagDto>((rel, tag) => rel.TagId == tag.Id)
diff --git a/src/Umbraco.Tests/Services/ContentServiceTagsTests.cs b/src/Umbraco.Tests/Services/ContentServiceTagsTests.cs
index 196af5c0bd..8f66e98b76 100644
--- a/src/Umbraco.Tests/Services/ContentServiceTagsTests.cs
+++ b/src/Umbraco.Tests/Services/ContentServiceTagsTests.cs
@@ -256,6 +256,53 @@ namespace Umbraco.Tests.Services
             Assert.IsFalse(enTagGroup.Any(x => x.Text == "plus"));
         }
 
+        [Test]
+        public void TagsCanBecomeInvariant2()
+        {
+            var languageService = ServiceContext.LocalizationService;
+            languageService.Save(new Language("fr-FR")); // en-US is already there
+
+            var enId = ServiceContext.LocalizationService.GetLanguageIdByIsoCode("en-US").Value;
+
+            var contentService = ServiceContext.ContentService;
+            var contentTypeService = ServiceContext.ContentTypeService;
+            var tagService = ServiceContext.TagService;
+            var contentType = MockedContentTypes.CreateSimpleContentType("umbMandatory", "Mandatory Doc Type", true);
+            PropertyType propertyType;
+            contentType.PropertyGroups.First().PropertyTypes.Add(
+                propertyType = new PropertyType("test", ValueStorageType.Ntext, "tags")
+                {
+                    DataTypeId = 1041,
+                    Variations = ContentVariation.Culture
+                });
+            contentType.Variations = ContentVariation.Culture;
+            contentTypeService.Save(contentType);
+
+            IContent content1 = MockedContent.CreateSimpleContent(contentType, "Tagged content 1", -1);
+            content1.SetCultureName("name-fr", "fr-FR");
+            content1.SetCultureName("name-en", "en-US");
+            content1.AssignTags("tags", new[] { "hello", "world", "some", "tags", "plus" }, culture: "fr-FR");
+            content1.AssignTags("tags", new[] { "hello", "world", "another", "one" }, culture: "en-US");
+            contentService.SaveAndPublish(content1);
+
+            IContent content2 = MockedContent.CreateSimpleContent(contentType, "Tagged content 2", -1);
+            content2.SetCultureName("name-fr", "fr-FR");
+            content2.SetCultureName("name-en", "en-US");
+            content2.AssignTags("tags", new[] { "hello", "world", "some", "tags", "plus" }, culture: "fr-FR");
+            content2.AssignTags("tags", new[] { "hello", "world", "another", "one" }, culture: "en-US");
+            contentService.SaveAndPublish(content2);
+
+            //// pretend we already have invariant values
+            //using (var scope = ScopeProvider.CreateScope())
+            //{
+            //    scope.Database.Execute("INSERT INTO [cmsTags] ([tag], [group], [languageId]) SELECT DISTINCT [tag], [group], NULL FROM [cmsTags] WHERE [languageId] IS NOT NULL");
+            //}
+
+            // this should work
+            propertyType.Variations = ContentVariation.Nothing;
+            Assert.DoesNotThrow(() => contentTypeService.Save(contentType));
+        }
+
         [Test]
         public void TagsCanBecomeInvariantByPropertyType()
         {