diff --git a/README.md b/README.md
index 385e6b0..b663f3f 100644
--- a/README.md
+++ b/README.md
@@ -54,6 +54,9 @@ fn main() {
     let duration = parse("3m + 31").unwrap(); //the default duration unit is second.
     assert_eq!(duration, Duration::new(211, 0));
 
+    let duration = parse("3m31s").unwrap();
+    assert_eq!(duration, Duration::new(211, 0));
+
     let duration = parse("3m + 13s + 29ms").unwrap();
     assert_eq!(duration, Duration::new(193, 29 * 1000 * 1000 + 0 + 0));
 
diff --git a/src/lib.rs b/src/lib.rs
index 2a57bd2..2e3cd93 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -214,10 +214,9 @@ trait ExpectErr<const LEN: usize> {
     fn expect_err<S: AsRef<str> + Display>(s: S) -> String;
 }
 
-#[derive(Debug, Eq, PartialEq, Clone, Default)]
+#[derive(Debug, Eq, PartialEq, Clone)]
 enum CondUnit {
     Plus,
-    #[default]
     Star,
 }
 
@@ -239,7 +238,7 @@ impl ExpectErr<2> for CondUnit {
     }
 
     fn expect_err<S: AsRef<str> + Display>(s: S) -> String {
-        format!("expect one of:['+','*'], but find:{}", s)
+        format!("expect one of:{:?}, but find:{}", Self::expect_val(), s)
     }
 }
 
diff --git a/src/parser.rs b/src/parser.rs
index d9807bd..ddf4cb4 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -150,6 +150,12 @@ mod tests {
         let duration = parse("1m+31").unwrap();
         assert_eq!(duration, Duration::new(91, 0));
 
+        let duration = parse("1m31").unwrap();
+        assert_eq!(duration, Duration::new(91, 0));
+
+        let duration = parse("1m31s").unwrap();
+        assert_eq!(duration, Duration::new(91, 0));
+
         let duration = parse("1m*60").unwrap();
         assert_eq!(duration, Duration::new(3600, 0));
 
@@ -187,7 +193,7 @@ partial_input:mxyz, expect one of :["y", "mon", "w", "d", "h", "m", "s", "ms", "
             r#"
 3ms-2ms
    ^
-partial_input:-2ms, expect one of:['+','*'], but find:-2ms"#
+partial_input:-2ms, expect one of:["+", "*"], but find:-2ms"#
                 .trim()
         );
     }