diff --git a/Source/uPSR_classes.pas b/Source/uPSR_classes.pas
index 2e17d9d..f46f070 100644
--- a/Source/uPSR_classes.pas
+++ b/Source/uPSR_classes.pas
@@ -624,15 +624,12 @@ procedure RIRegisterTSTREAM(Cl: TPSRuntimeClassImporter);
 begin
   with Cl.Add(TSTREAM) do
   begin
-    {$IFNDEF DELPHI_SYDNEY_UP}
+    { uPSC_Classes doesn't turn on IsAbstract on Sydney and newer but here we
+      still use RegisterVirtualAbstractMethod because with RegisterVirtualMethod
+      it picks the wrong overload, at least for Seek }
     RegisterVirtualAbstractMethod(TMemoryStream, @TMemoryStream.READ, 'Read');
     RegisterVirtualAbstractMethod(TMemoryStream, @TMemoryStream.WRITE, 'Write');
     RegisterVirtualAbstractMethod(TMemoryStream, @TMemoryStream.SEEK, 'Seek');
-    {$ELSE}
-    RegisterVirtualMethod(@TStream.READ, 'Read');
-    RegisterVirtualMethod(@TStream.WRITE, 'Write');
-    RegisterVirtualMethod(@TStream.SEEK, 'Seek');
-    {$ENDIF}
     RegisterMethod(@TSTREAM.READBUFFER, 'ReadBuffer');
     RegisterMethod(@TSTREAM.WRITEBUFFER, 'WriteBuffer');
     RegisterMethod(@TSTREAM.COPYFROM, 'CopyFrom');