diff --git a/src/swab.rs b/src/swab.rs
index 3bb40a5..7889a59 100644
--- a/src/swab.rs
+++ b/src/swab.rs
@@ -50,7 +50,7 @@ fn main() -> ExitCode {
 
 	let mut wordsize: usize = 2;
 
-	while let Some(opt) = argv.getopt("w:") {
+	while let Some(opt) = argv.getopt(":w:") {
 		match opt.opt() {
 			Ok("w") => {
 				if let Some(arg) = opt.arg() {