diff --git a/01_phase_rust_src/sv/src/main.rs b/01_phase_rust_src/sv/src/main.rs
index eeac18b..8f722c3 100644
--- a/01_phase_rust_src/sv/src/main.rs
+++ b/01_phase_rust_src/sv/src/main.rs
@@ -55,6 +55,10 @@ fn main() {
                 i += 1;
             }
             else {
+                if val.len() == 2 { 
+                    println!("sv: illegal option -- {}", val.chars().nth(1).unwrap() );
+                    // TODO: thread NOT pannic if it is not an ASCII character.
+                }
                 parser::misc::usage();
                 exit(100);
             }