diff --git a/owlps-positioning/src/direction.cc b/owlps-positioning/src/direction.cc
index 2c017d6..8d4da53 100644
--- a/owlps-positioning/src/direction.cc
+++ b/owlps-positioning/src/direction.cc
@@ -21,7 +21,7 @@ Direction::Direction(const char source):
 
 inline void Direction::assert_valid() const
 {
-  if (! is_valid())
+  if (! (is_valid() || direction == 0))
     throw bad_direction(direction) ;
 }