--- a/inst/helscanintrlv.m
+++ b/inst/helscanintrlv.m
@@ -61,3 +61,10 @@
   endif
 
 endfunction
+
+%% Test input validation
+%!error helscanintrlv ()
+%!error helscanintrlv (1)
+%!error helscanintrlv (1, 2)
+%!error helscanintrlv (1, 2, 3)
+%!error helscanintrlv (1, 2, 3, 4, 5)