diff --git a/Packages/Interval_arithmetic/examples/Interval_arithmetic/filtered_predicate_converter b/Packages/Interval_arithmetic/examples/Interval_arithmetic/filtered_predicate_converter
index 99306f7e767..4a958994ce4 100755
--- a/Packages/Interval_arithmetic/examples/Interval_arithmetic/filtered_predicate_converter
+++ b/Packages/Interval_arithmetic/examples/Interval_arithmetic/filtered_predicate_converter
@@ -35,6 +35,13 @@ while (<>)
     $after_template=0;
     $in_decl=0;
     $in_def=1;
+    if (($result_type ne "CGAL_Sign") &&
+        ($result_type ne "bool") &&
+        ($result_type ne "CGAL_Comparison_result") &&
+        ($result_type ne "CGAL_Orientation") &&
+        ($result_type ne "CGAL_Oriented_side") &&
+        ($result_type ne "CGAL_Bounded_side"))
+      {print STDERR "Warning: $result_type is unknown\n"; }
     print
 "{ // This is the default filter (specialization).\n
   $result_type result;