diff --git a/rrule/src/core/rrule.rs b/rrule/src/core/rrule.rs
index b3fadde..3ea9838 100644
--- a/rrule/src/core/rrule.rs
+++ b/rrule/src/core/rrule.rs
@@ -656,7 +656,7 @@ impl<S> Display for RRule<S> {
 
         // Monday is the default, no need to expose it.
         if self.week_start != Weekday::Mon {
-            res.push(format!("WKST={}", &self.week_start));
+            res.push(format!("WKST={}", weekday_to_str(self.week_start)));
         }
 
         if !self.by_set_pos.is_empty() {
diff --git a/rrule/src/tests/regression.rs b/rrule/src/tests/regression.rs
index debfbc2..1342045 100644
--- a/rrule/src/tests/regression.rs
+++ b/rrule/src/tests/regression.rs
@@ -1,7 +1,7 @@
 use chrono::Month;
 
 use crate::tests::common;
-use crate::{Frequency, RRule, RRuleSet};
+use crate::{Frequency, RRule, RRuleSet, Unvalidated};
 
 #[test]
 fn issue_34() {
@@ -60,3 +60,13 @@ fn issue_97() {
         "FREQ=YEARLY;BYMONTH=12;BYMONTHDAY=24,25,26"
     );
 }
+
+#[test]
+fn issue_111() {
+    let rrule = "RRULE:FREQ=WEEKLY;INTERVAL=1;BYDAY=TU;WKST=SU"
+        .parse::<RRule<Unvalidated>>();
+
+        // Convert to string...
+    let rrule_str = format!("{}", rrule.unwrap());
+    assert!(rrule_str.contains("WKST=SU"));
+}
\ No newline at end of file