diff --git a/src/HistoryWindow.cpp b/src/HistoryWindow.cpp
index 10b0f6e6a..a135b133f 100644
--- a/src/HistoryWindow.cpp
+++ b/src/HistoryWindow.cpp
@@ -40,11 +40,13 @@ undo memory so as to free up space.
 #include "../images/Empty9x16.xpm"
 #include "UndoManager.h"
 #include "Project.h"
+#include "ProjectFileIO.h"
 #include "ProjectHistory.h"
 #include "ShuttleGui.h"
 
 enum {
    ID_AVAIL = 1000,
+   ID_FILESIZE,
    ID_TOTAL,
    ID_LEVELS,
    ID_DISCARD,
@@ -98,6 +100,11 @@ HistoryDialog::HistoryDialog(AudacityProject *parent, UndoManager *manager):
 
          S.StartMultiColumn(3, wxCENTRE);
          {
+            mFileSize = S.Id(ID_FILESIZE)
+               .ConnectRoot(wxEVT_KEY_DOWN, &HistoryDialog::OnChar)
+               .AddTextBox(XXO("&Project file size"), wxT("0"), 10);
+            S.AddVariableText( {} )->Hide();
+
             mTotal = S.Id(ID_TOTAL)
                .ConnectRoot(wxEVT_KEY_DOWN, &HistoryDialog::OnChar)
                .AddTextBox(XXO("&Total space used"), wxT("0"), 10);
@@ -201,6 +208,10 @@ void HistoryDialog::DoUpdate()
 
    mList->DeleteAllItems();
 
+   wxFileName filename(ProjectFileIO::Get(*mProject).GetFileName());
+   wxULongLong_t filesize = filename.GetSize().GetValue();
+   mFileSize->SetValue(Internat::FormatSize(filesize).Translation());
+
    wxLongLong_t total = 0;
    mSelected = mManager->GetCurrentState() - 1;
    for (i = 0; i < (int)mManager->GetNumStates(); i++) {
diff --git a/src/HistoryWindow.h b/src/HistoryWindow.h
index e86eb3fc6..089b95ae5 100644
--- a/src/HistoryWindow.h
+++ b/src/HistoryWindow.h
@@ -46,6 +46,7 @@ class HistoryDialog final : public wxDialogWrapper {
    AudacityProject   *mProject;
    UndoManager       *mManager;
    wxListCtrl        *mList;
+   wxTextCtrl        *mFileSize;
    wxTextCtrl        *mTotal;
    wxTextCtrl        *mClipboard;
    wxTextCtrl        *mAvail;
diff --git a/src/ProjectFileIO.cpp b/src/ProjectFileIO.cpp
index b8dd70183..f4c2bcdc3 100644
--- a/src/ProjectFileIO.cpp
+++ b/src/ProjectFileIO.cpp
@@ -27,6 +27,7 @@ Paul Licameli split from AudacityProject.cpp
 #include "SampleBlock.h"
 #include "Sequence.h"
 #include "Tags.h"
+#include "TimeTrack.h"
 #include "ViewInfo.h"
 #include "WaveClip.h"
 #include "WaveTrack.h"
diff --git a/src/UndoManager.cpp b/src/UndoManager.cpp
index f2f7f9f31..f606832e1 100644
--- a/src/UndoManager.cpp
+++ b/src/UndoManager.cpp
@@ -44,8 +44,8 @@ wxDEFINE_EVENT(EVT_UNDO_MODIFIED, wxCommandEvent);
 wxDEFINE_EVENT(EVT_UNDO_OR_REDO, wxCommandEvent);
 wxDEFINE_EVENT(EVT_UNDO_RESET, wxCommandEvent);
 
-using ConstSampleBlockPtr = const SampleBlock*;
-using Set = std::unordered_set<ConstSampleBlockPtr>;
+using SampleBlockID = long long;
+using Set = std::unordered_set<SampleBlockID>;
 
 struct UndoStackElem {
 
@@ -112,7 +112,7 @@ namespace {
 
                // Accumulate space used by the file if the file was not
                // yet seen
-               if ( !seen || (seen->count( &*sb ) == 0 ) )
+               if ( !seen || (seen->count( sb->GetBlockID() ) == 0 ) )
                {
                   unsigned long long usage{ sb->GetSpaceUsage() };
                   result += usage;
@@ -120,7 +120,7 @@ namespace {
 
                // Add file to current set
                if (seen)
-                  seen->insert( &*sb );
+                  seen->insert( sb->GetBlockID() );
             }
          }
       }