diff --git a/libsrc/csg/surface.cpp b/libsrc/csg/surface.cpp
index cb6ab48b..6231897b 100644
--- a/libsrc/csg/surface.cpp
+++ b/libsrc/csg/surface.cpp
@@ -16,6 +16,7 @@ Surface :: Surface ()
   strcpy (name, "noname");
   bcprop = -1;
   bcname = "default";
+  inverse = false;
 }
 
 Surface :: ~Surface()