diff --git a/.gitignore b/.gitignore
index d00a2b5d..dad583c5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,6 +4,7 @@
 *.app
 *.user
 *.rej
+.cache
 
 moc_*.cpp
 ui_*.h
@@ -15,9 +16,8 @@ qrc_*.cpp
 
 rc_price_list.py
 CPackConfig.cmake
-
-configure.sh
-configure.bat
+CMakeUserPresets.json
+compile_commands.json
 
 bin/
 lib/
diff --git a/docs/CHANGES_2_4.txt b/docs/CHANGES_2_4.txt
index 96ad0e00..5d753636 100644
--- a/docs/CHANGES_2_4.txt
+++ b/docs/CHANGES_2_4.txt
@@ -7,7 +7,7 @@ General:
 
 Bugfixes:
 -------------
-*
+* Fix undefined behaviour (invalid int-to-enum cast) in AbstractTableElementPrivate::fillConstraints, detected by UBSAN.
 
 New features:
 -------------
diff --git a/src/KDReports/KDReportsAbstractTableElement.cpp b/src/KDReports/KDReportsAbstractTableElement.cpp
index 3a186b4a..db6f5088 100644
--- a/src/KDReports/KDReportsAbstractTableElement.cpp
+++ b/src/KDReports/KDReportsAbstractTableElement.cpp
@@ -124,13 +124,15 @@ void KDReports::AbstractTableElementPrivate::fillConstraints(QTextTableFormat *t
         constraints.reserve(m_constraints.size());
         for (const auto &c : m_constraints) {
             QTextLength length; // Variable by default
-            switch (c.unit) {
-            case Millimeters:
-                length = QTextLength(QTextLength::FixedLength, mmToPixels(c.width));
-                break;
-            case Percent:
-                length = QTextLength(QTextLength::PercentageLength, c.width);
-                break;
+            if (c.unit.has_value()) {
+                switch (*c.unit) {
+                case Millimeters:
+                    length = QTextLength(QTextLength::FixedLength, mmToPixels(c.width));
+                    break;
+                case Percent:
+                    length = QTextLength(QTextLength::PercentageLength, c.width);
+                    break;
+                }
             }
             constraints.append(length);
         }
diff --git a/src/KDReports/KDReportsAbstractTableElement.h b/src/KDReports/KDReportsAbstractTableElement.h
index 8b8bfac9..98792f0d 100644
--- a/src/KDReports/KDReportsAbstractTableElement.h
+++ b/src/KDReports/KDReportsAbstractTableElement.h
@@ -13,6 +13,7 @@
 
 #include "KDReportsElement.h"
 #include "KDReportsUnit.h"
+#include <optional>
 
 QT_BEGIN_NAMESPACE
 template<typename T>
@@ -105,16 +106,10 @@ class KDREPORTS_EXPORT AbstractTableElement : public Element
      */
     QFont defaultFont(bool *isSet) const;
 
-    enum // separate because we don't want "Variable" in other uses of Unit
-    {
-        Variable = Unit::Percent + 1 /// < no constraint, \since 2.3
-    };
-
     struct ColumnConstraint
     {
         ColumnConstraint()
             : width(0)
-            , unit(static_cast<Unit>(Variable))
         {
         }
         ColumnConstraint(qreal w, Unit u)
@@ -123,7 +118,7 @@ class KDREPORTS_EXPORT AbstractTableElement : public Element
         {
         }
         qreal width;
-        Unit unit;
+        std::optional<Unit> unit;
     };
 
     /**