diff --git a/src/Microsoft.OpenApi/Models/OpenApiDocument.cs b/src/Microsoft.OpenApi/Models/OpenApiDocument.cs
index 0ac0c1941..62a1afa22 100644
--- a/src/Microsoft.OpenApi/Models/OpenApiDocument.cs
+++ b/src/Microsoft.OpenApi/Models/OpenApiDocument.cs
@@ -89,6 +89,7 @@ public ISet<OpenApiTag>? Tags
             {
                 if (value is null)
                 {
+                    _tags = null;
                     return;
                 }
                 _tags = value switch
diff --git a/test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.cs b/test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.cs
index 7a47b8597..f7095bd31 100644
--- a/test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.cs
+++ b/test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.cs
@@ -2145,6 +2145,17 @@ public void TagsSupportsCustomComparer()
             Assert.Equal(2, document.Tags.Count);
         }
 
+        [Fact]
+        public void TagsCanBeReInitializedToNull()
+        {
+            var document = new OpenApiDocument();
+            Assert.Null(document.Tags);
+            document.Tags = new HashSet<OpenApiTag>();
+            Assert.NotNull(document.Tags);
+            document.Tags = null;
+            Assert.Null(document.Tags);
+        }
+
         private sealed class CaseInsensitiveOpenApiTagEqualityComparer : IEqualityComparer<OpenApiTag>
         {
             public bool Equals(OpenApiTag x, OpenApiTag y)