diff --git a/src/chrono/date.rs b/src/chrono/date.rs
index 770e08c5..a36c73ff 100644
--- a/src/chrono/date.rs
+++ b/src/chrono/date.rs
@@ -701,10 +701,10 @@ mod tests {
 
     #[test]
     fn test_date_fmt() {
-        assert_eq!(DateZ::from_ymd(2012,  3, 4).unwrap().to_str(),  "2012-03-04".to_owned());
-        assert_eq!(DateZ::from_ymd(0,     3, 4).unwrap().to_str(),  "0000-03-04".to_owned());
-        assert_eq!(DateZ::from_ymd(-307,  3, 4).unwrap().to_str(), "-0307-03-04".to_owned());
-        assert_eq!(DateZ::from_ymd(12345, 3, 4).unwrap().to_str(), "+12345-03-04".to_owned());
+        assert_eq!(DateZ::from_ymd(2012,  3, 4).unwrap().to_str(),  "2012-03-04".to_string());
+        assert_eq!(DateZ::from_ymd(0,     3, 4).unwrap().to_str(),  "0000-03-04".to_string());
+        assert_eq!(DateZ::from_ymd(-307,  3, 4).unwrap().to_str(), "-0307-03-04".to_string());
+        assert_eq!(DateZ::from_ymd(12345, 3, 4).unwrap().to_str(), "+12345-03-04".to_string());
     }
 }
 
diff --git a/src/chrono/duration.rs b/src/chrono/duration.rs
index 43b6bfba..f15e65d9 100644
--- a/src/chrono/duration.rs
+++ b/src/chrono/duration.rs
@@ -391,15 +391,15 @@ mod tests {
 
     #[test]
     fn test_duration_fmt() {
-        assert_eq!(Duration::zero().to_str(), "PT0S".to_owned());
-        assert_eq!(Duration::days(42).to_str(), "P42D".to_owned());
-        assert_eq!(Duration::days(-42).to_str(), "P-42D".to_owned());
-        assert_eq!(Duration::seconds(42).to_str(), "PT42S".to_owned());
-        assert_eq!(Duration::milliseconds(42).to_str(), "PT0,042S".to_owned());
-        assert_eq!(Duration::microseconds(42).to_str(), "PT0,000042S".to_owned());
-        assert_eq!(Duration::nanoseconds(42).to_str(), "PT0,000000042S".to_owned());
+        assert_eq!(Duration::zero().to_str(), "PT0S".to_string());
+        assert_eq!(Duration::days(42).to_str(), "P42D".to_string());
+        assert_eq!(Duration::days(-42).to_str(), "P-42D".to_string());
+        assert_eq!(Duration::seconds(42).to_str(), "PT42S".to_string());
+        assert_eq!(Duration::milliseconds(42).to_str(), "PT0,042S".to_string());
+        assert_eq!(Duration::microseconds(42).to_str(), "PT0,000042S".to_string());
+        assert_eq!(Duration::nanoseconds(42).to_str(), "PT0,000000042S".to_string());
         assert_eq!((Duration::days(7) + Duration::milliseconds(6543)).to_str(),
-                   "P7DT6,543S".to_owned());
+                   "P7DT6,543S".to_string());
     }
 }
 
diff --git a/src/chrono/time.rs b/src/chrono/time.rs
index cd978f51..42c81573 100644
--- a/src/chrono/time.rs
+++ b/src/chrono/time.rs
@@ -258,13 +258,13 @@ mod tests {
 
     #[test]
     fn test_time_fmt() {
-        assert_eq!(hmsm(23, 59, 59,   999).to_str(), "23:59:59,999".to_owned());
-        assert_eq!(hmsm(23, 59, 59, 1_000).to_str(), "23:59:60".to_owned());
-        assert_eq!(hmsm(23, 59, 59, 1_001).to_str(), "23:59:60,001".to_owned());
+        assert_eq!(hmsm(23, 59, 59,   999).to_str(), "23:59:59,999".to_string());
+        assert_eq!(hmsm(23, 59, 59, 1_000).to_str(), "23:59:60".to_string());
+        assert_eq!(hmsm(23, 59, 59, 1_001).to_str(), "23:59:60,001".to_string());
         assert_eq!(TimeZ::from_hms_micro(0, 0, 0, 43210).unwrap().to_str(),
-                   "00:00:00,043210".to_owned());
+                   "00:00:00,043210".to_string());
         assert_eq!(TimeZ::from_hms_nano(0, 0, 0, 6543210).unwrap().to_str(),
-                   "00:00:00,006543210".to_owned());
+                   "00:00:00,006543210".to_string());
     }
 }