diff --git a/src/legend/qarealegendmarker.h b/src/legend/qarealegendmarker.h
index 84203e2..55c06b9 100644
--- a/src/legend/qarealegendmarker.h
+++ b/src/legend/qarealegendmarker.h
@@ -41,7 +41,7 @@ public:
     virtual LegendMarkerType type() { return LegendMarkerTypeArea; }
 
     // Related series
-    QAreaSeries* series();
+    virtual QAreaSeries* series();
 
 protected:
     QAreaLegendMarker(QAreaLegendMarkerPrivate &d, QObject *parent = 0);
diff --git a/src/legend/qbarlegendmarker.h b/src/legend/qbarlegendmarker.h
index 511444e..88abc06 100644
--- a/src/legend/qbarlegendmarker.h
+++ b/src/legend/qbarlegendmarker.h
@@ -40,7 +40,7 @@ public:
     virtual LegendMarkerType type() { return LegendMarkerTypeBar; }
 
     // Related series and barset
-    QAbstractBarSeries* series();
+    virtual QAbstractBarSeries* series();
     QBarSet* barset();
 
 protected:
diff --git a/src/legend/qlegendmarker.h b/src/legend/qlegendmarker.h
index bdf5678..5f23612 100644
--- a/src/legend/qlegendmarker.h
+++ b/src/legend/qlegendmarker.h
@@ -72,6 +72,8 @@ public:
     bool isVisible() const;
     void setVisible(bool visible);
 
+    virtual QAbstractSeries* series() = 0;
+
 protected:
     explicit QLegendMarker(QLegendMarkerPrivate &d, QObject *parent = 0);
 
diff --git a/src/legend/qpielegendmarker.h b/src/legend/qpielegendmarker.h
index 6aa5947..47e0e21 100644
--- a/src/legend/qpielegendmarker.h
+++ b/src/legend/qpielegendmarker.h
@@ -42,7 +42,7 @@ public:
     virtual LegendMarkerType type() { return LegendMarkerTypePie; }
 
     // Related series and slice
-    QPieSeries* series();
+    virtual QPieSeries* series();
     QPieSlice* slice();
 
 protected:
diff --git a/src/legend/qxylegendmarker.h b/src/legend/qxylegendmarker.h
index 593a8cb..5a29e48 100644
--- a/src/legend/qxylegendmarker.h
+++ b/src/legend/qxylegendmarker.h
@@ -39,7 +39,7 @@ public:
     virtual LegendMarkerType type() { return LegendMarkerTypeXY; }
 
     // Related series
-    QXYSeries* series();
+    virtual QXYSeries* series();
 
 protected:
     QXYLegendMarker(QXYLegendMarkerPrivate &d, QObject *parent = 0);