diff --git a/STL_Extension/include/CGAL/Uncertain.h b/STL_Extension/include/CGAL/Uncertain.h
index 196b642f558..adadc213ace 100644
--- a/STL_Extension/include/CGAL/Uncertain.h
+++ b/STL_Extension/include/CGAL/Uncertain.h
@@ -69,7 +69,7 @@ namespace internal {
 
 // Exception type for the automatic conversion.
 class Uncertain_conversion_exception
-  : std::range_error
+  : public std::range_error
 {
 public:
   Uncertain_conversion_exception(const std::string &s)