diff --git a/include/openmc/position.h b/include/openmc/position.h
index e49958fe34..a0106b5f26 100644
--- a/include/openmc/position.h
+++ b/include/openmc/position.h
@@ -58,7 +58,7 @@ struct Position {
   }
 
   // Data members
-  union{ double xyz[3]; struct{ double x,y,z; }; };
+  union{ double xyz[3]; struct{ double x,y,z = 0.0; }; };
 };
 
 // Binary operators