diff --git a/simgear/math/SGSphere.hxx b/simgear/math/SGSphere.hxx
index 7d8b3ab1..7d6a8d3c 100644
--- a/simgear/math/SGSphere.hxx
+++ b/simgear/math/SGSphere.hxx
@@ -22,6 +22,7 @@ template<typename T>
 class SGSphere {
 public:
   SGSphere() :
+    _center(0.0, 0.0, 0.0),
     _radius(-1)
   { }
   SGSphere(const SGVec3<T>& center, const T& radius) :