diff --git a/source/mysqlquerythread.pas b/source/mysqlquerythread.pas
index 92763f96..38848a8e 100644
--- a/source/mysqlquerythread.pas
+++ b/source/mysqlquerythread.pas
@@ -338,7 +338,7 @@ begin
     on E: Exception do begin
       if E.Message = SCanNotOpenResultSet then begin
         Result := true;
-        ADataset := nil;
+        FreeAndNil(ADataset);
       end else AExceptionData := GetExceptionData(E);
     end;
   end;