diff --git a/source/integer_to_roman/mod.rs b/source/integer_to_roman/mod.rs
index 6ea4ea5..5cc3bbf 100644
--- a/source/integer_to_roman/mod.rs
+++ b/source/integer_to_roman/mod.rs
@@ -14,7 +14,7 @@ pub fn int_to_roman(number: i32) -> String {
       10 => ("X", "L", "C"),
       100 => ("C", "D", "M"),
       1000 => ("M", "", ""),
-      _ => ("", "", ""),
+      _ => unreachable!(),
     };
 
     result += &match digit {