diff --git a/src/Npgsql/NpgsqlDataSourceBuilder.cs b/src/Npgsql/NpgsqlDataSourceBuilder.cs
index b08f175533..b18ce75848 100644
--- a/src/Npgsql/NpgsqlDataSourceBuilder.cs
+++ b/src/Npgsql/NpgsqlDataSourceBuilder.cs
@@ -415,6 +415,7 @@ public NpgsqlDataSourceBuilder UseNegotiateOptionsCallback(Action<NegotiateAuthe
     #region Type mapping
 
     /// <inheritdoc />
+    [Experimental(NpgsqlDiagnostics.ConvertersExperimental)]
     public void AddTypeInfoResolverFactory(PgTypeInfoResolverFactory factory)
         => _internalBuilder.AddTypeInfoResolverFactory(factory);
 
diff --git a/src/Npgsql/NpgsqlSlimDataSourceBuilder.cs b/src/Npgsql/NpgsqlSlimDataSourceBuilder.cs
index 8bfe449c4a..9f91ef66b2 100644
--- a/src/Npgsql/NpgsqlSlimDataSourceBuilder.cs
+++ b/src/Npgsql/NpgsqlSlimDataSourceBuilder.cs
@@ -532,6 +532,7 @@ public bool UnmapComposite([DynamicallyAccessedMembers(DynamicallyAccessedMember
         => _userTypeMapper.UnmapComposite(clrType, pgName, nameTranslator);
 
     /// <inheritdoc />
+    [Experimental(NpgsqlDiagnostics.ConvertersExperimental)]
     public void AddTypeInfoResolverFactory(PgTypeInfoResolverFactory factory) => _resolverChainBuilder.PrependResolverFactory(factory);
 
     /// <inheritdoc />
diff --git a/src/Npgsql/TypeMapping/INpgsqlTypeMapper.cs b/src/Npgsql/TypeMapping/INpgsqlTypeMapper.cs
index b5f2de7594..cbb6ac8ccc 100644
--- a/src/Npgsql/TypeMapping/INpgsqlTypeMapper.cs
+++ b/src/Npgsql/TypeMapping/INpgsqlTypeMapper.cs
@@ -196,6 +196,7 @@ bool UnmapComposite(
     /// Typically used by plugins.
     /// </summary>
     /// <param name="factory">The type resolver factory to be added.</param>
+    [Experimental(NpgsqlDiagnostics.ConvertersExperimental)]
     void AddTypeInfoResolverFactory(PgTypeInfoResolverFactory factory);
 
     /// <summary>