diff --git a/simgear/props/propertyObject.hxx b/simgear/props/propertyObject.hxx
index 90e0101a..28623211 100644
--- a/simgear/props/propertyObject.hxx
+++ b/simgear/props/propertyObject.hxx
@@ -157,6 +157,8 @@ template <>
 class PropertyObject<std::string> : PropertyObjectBase
 {
 public:
+  PropertyObject() = default;
+
   explicit PropertyObject(const char* aChild) :
     PropertyObjectBase(aChild)
   { }