diff --git a/src/Mod/Spreadsheet/App/PropertySheet.cpp b/src/Mod/Spreadsheet/App/PropertySheet.cpp
index 1a3021903..bd8c9318c 100644
--- a/src/Mod/Spreadsheet/App/PropertySheet.cpp
+++ b/src/Mod/Spreadsheet/App/PropertySheet.cpp
@@ -764,7 +764,7 @@ void PropertySheet::removeColumns(int col, int count)
     }
 }
 
-unsigned int PropertySheet::getMemSize()
+unsigned int PropertySheet::getMemSize() const
 {
     return sizeof(*this);
 }
diff --git a/src/Mod/Spreadsheet/App/PropertySheet.h b/src/Mod/Spreadsheet/App/PropertySheet.h
index c718d549d..bc7d9ddc8 100644
--- a/src/Mod/Spreadsheet/App/PropertySheet.h
+++ b/src/Mod/Spreadsheet/App/PropertySheet.h
@@ -105,7 +105,7 @@ public:
 
     void removeColumns(int col, int count);
 
-    unsigned int getMemSize (void);
+    virtual unsigned int getMemSize (void) const;
 
     bool mergeCells(CellAddress from, CellAddress to);