diff -r e82d852e4fb0 lib/intersect_face_division.cpp
--- a/lib/intersect_face_division.cpp	Wed Jan 15 13:16:14 2014 +1100
+++ b/lib/intersect_face_division.cpp	Wed Mar 12 23:09:19 2014 +0600
@@ -1121,7 +1121,9 @@
         }
 
         // copy up to the end of the path.
-        std::copy(base_loop.begin() + pos, base_loop.begin() + e1_1, std::back_inserter(out));
+        if (pos < e1_1) {
+            std::copy(base_loop.begin() + pos, base_loop.begin() + e1_1, std::back_inserter(out));
+        }
 
         CARVE_ASSERT(base_loop[e1_1] == p1.back());
         std::copy(p1.rbegin(), p1.rend() - 1, std::back_inserter(out));