diff --git a/atsynedit/atstrings.pas b/atsynedit/atstrings.pas
index 15e7ddb59..d34169fd0 100644
--- a/atsynedit/atstrings.pas
+++ b/atsynedit/atstrings.pas
@@ -1619,6 +1619,7 @@ procedure TATStrings.DoUndoSingle(ACurList: TATUndoList;
   ALineState: TATLineState;
   ACarets: TATPointArray;
   NCount: integer;
+  OtherList: TATUndoList;
 begin
   ASoftMarked:= true;
   AHardMarked:= false;
@@ -1642,6 +1643,11 @@ procedure TATStrings.DoUndoSingle(ACurList: TATUndoList;
   AHardMarkedNext:= (NCount>1) and (ACurList[NCount-2].ItemHardMark);
   AUnmodifiedNext:= (NCount>1) and (ACurList[NCount-2].ItemAction=aeaClearModified);
 
+  if ACurList=FUndoList then
+    OtherList:= FRedoList
+  else
+    OtherList:= FUndoList;
+
   //don't undo if one item left: unmodified-mark
   if ACurList.IsEmpty then exit;
 
@@ -1680,11 +1686,7 @@ procedure TATStrings.DoUndoSingle(ACurList: TATUndoList;
 
       aeaClearModified:
         begin
-          //add unmodified mark to undo/redo
-          if ACurList=FUndoList then
-            FRedoList.AddUnmodifiedMark
-          else
-            FUndoList.AddUnmodifiedMark;
+          OtherList.AddUnmodifiedMark;
           exit;
         end