diff --git a/helix-core/src/shellwords.rs b/helix-core/src/shellwords.rs
index 44c7a48a2a50..641991ef2195 100644
--- a/helix-core/src/shellwords.rs
+++ b/helix-core/src/shellwords.rs
@@ -976,6 +976,25 @@ mod test {
         assert_eq!(Some("ENV_PATH"), args.get_flag::<&str>("env").unwrap());
     }
 
+    #[test]
+    fn should_error_on_unknown_flag() {
+        let shellwords = Shellwords::from(":w --foo");
+        let args = Args::from_signature(
+            shellwords.args(),
+            ParseMode::Parameters,
+            &[Flag {
+                long: "no-format",
+                short: None,
+                desc: "test",
+                accepts: None,
+                completer: None,
+            }],
+        );
+
+        assert_eq!(":w", shellwords.command());
+        assert!(args.is_err());
+    }
+
     #[test]
     fn should_split_args_no_slash_unescaping() {
         let input = r#"single_word twó wörds \\three\ \"with\ escaping\\"#;