diff --git a/src/chrono/date.rs b/src/chrono/date.rs
index 050aac2..a9037d6 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");
-        assert_eq!(DateZ::from_ymd(0,     3, 4).unwrap().to_str(),  ~"0000-03-04");
-        assert_eq!(DateZ::from_ymd(-307,  3, 4).unwrap().to_str(), ~"-0307-03-04");
-        assert_eq!(DateZ::from_ymd(12345, 3, 4).unwrap().to_str(), ~"+12345-03-04");
+        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());
     }
 }
 
diff --git a/src/chrono/duration.rs b/src/chrono/duration.rs
index 55372b8..6096185 100644
--- a/src/chrono/duration.rs
+++ b/src/chrono/duration.rs
@@ -391,14 +391,15 @@ mod tests {
 
     #[test]
     fn test_duration_fmt() {
-        assert_eq!(Duration::zero().to_str(), ~"PT0S");
-        assert_eq!(Duration::days(42).to_str(), ~"P42D");
-        assert_eq!(Duration::days(-42).to_str(), ~"P-42D");
-        assert_eq!(Duration::seconds(42).to_str(), ~"PT42S");
-        assert_eq!(Duration::milliseconds(42).to_str(), ~"PT0,042S");
-        assert_eq!(Duration::microseconds(42).to_str(), ~"PT0,000042S");
-        assert_eq!(Duration::nanoseconds(42).to_str(), ~"PT0,000000042S");
-        assert_eq!((Duration::days(7) + Duration::milliseconds(6543)).to_str(), ~"P7DT6,543S");
+        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::days(7) + Duration::milliseconds(6543)).to_str(),
+                   "P7DT6,543S".to_owned());
     }
 }
 
diff --git a/src/chrono/time.rs b/src/chrono/time.rs
index 3235adf..b98bebb 100644
--- a/src/chrono/time.rs
+++ b/src/chrono/time.rs
@@ -258,11 +258,13 @@ mod tests {
 
     #[test]
     fn test_time_fmt() {
-        assert_eq!(hmsm(23, 59, 59,   999).to_str(), ~"23:59:59,999");
-        assert_eq!(hmsm(23, 59, 59, 1_000).to_str(), ~"23:59:60");
-        assert_eq!(hmsm(23, 59, 59, 1_001).to_str(), ~"23:59:60,001");
-        assert_eq!(TimeZ::from_hms_micro(0, 0, 0, 43210).unwrap().to_str(), ~"00:00:00,043210");
-        assert_eq!(TimeZ::from_hms_nano(0, 0, 0, 6543210).unwrap().to_str(), ~"00:00:00,006543210");
+        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!(TimeZ::from_hms_micro(0, 0, 0, 43210).unwrap().to_str(),
+                   "00:00:00,043210".to_owned());
+        assert_eq!(TimeZ::from_hms_nano(0, 0, 0, 6543210).unwrap().to_str(),
+                   "00:00:00,006543210".to_owned());
     }
 }