diff --git a/src/osgVolume/Property.cpp b/src/osgVolume/Property.cpp
index 191dc9bda..c0b24798d 100644
--- a/src/osgVolume/Property.cpp
+++ b/src/osgVolume/Property.cpp
@@ -52,7 +52,7 @@ void CompositeProperty::clear()
 //
 // SwitchProperty
 //
-SwitchProperty::SwitchProperty()
+SwitchProperty::SwitchProperty():_activeProperty(0)
 {
 }