1 files changed, 7 insertions, 2 deletions
diff --git a/src/2geom/utils.h b/src/2geom/utils.h
index a96a34dff..50dfa82fe 100644
--- a/src/2geom/utils.h
+++ b/src/2geom/utils.h
@@ -1,5 +1,5 @@
-#ifndef UTILS_HEADER
-#define UTILS_HEADER
+#ifndef LIB2GEOM_UTILS_HEADER
+#define LIB2GEOM_UTILS_HEADER
 
 /** Various utility functions.
  *
@@ -40,6 +40,11 @@ public:
   NotImplemented() : std::logic_error("method not implemented") {}
 };
 
+class NotInvertible : public std::range_error {
+ public:
+  NotInvertible() : std::range_error("function does not have a unique inverse") {}
+};
+
 // proper logical xor
 inline bool logical_xor (bool a, bool b) { return (a || b) && !(a && b); }