diff --git a/src/uu/date/src/date.rs b/src/uu/date/src/date.rs
index 3c9488e7f..8ff6283c5 100644
--- a/src/uu/date/src/date.rs
+++ b/src/uu/date/src/date.rs
@@ -314,6 +314,7 @@ pub fn uu_app() -> Command {
             Arg::new(OPT_RFC_3339)
                 .long(OPT_RFC_3339)
                 .value_name("FMT")
+                .value_parser([DATE, SECOND, SECONDS, NS])
                 .help(RFC_3339_HELP_STRING),
         )
         .arg(
diff --git a/tests/by-util/test_date.rs b/tests/by-util/test_date.rs
index 7451574ff..1727f4006 100644
--- a/tests/by-util/test_date.rs
+++ b/tests/by-util/test_date.rs
@@ -43,6 +43,13 @@ fn test_date_rfc_3339() {
     }
 }
 
+#[test]
+fn test_date_rfc_3339_invalid_arg() {
+    for param in ["--iso-3339", "--rfc-3"] {
+        new_ucmd!().arg(format!("{param}=foo")).fails();
+    }
+}
+
 #[test]
 fn test_date_rfc_8601_default() {
     let re = Regex::new(r"^\d{4}-\d{2}-\d{2}\n$").unwrap();