diff --git a/src/libcollections/hash/sip.rs b/src/libcollections/hash/sip.rs
index ab182bd5602..4ac06a884a6 100644
--- a/src/libcollections/hash/sip.rs
+++ b/src/libcollections/hash/sip.rs
@@ -402,7 +402,7 @@ mod tests {
             debug!("siphash test {}: {}", t, buf);
             let vec = u8to64_le!(vecs[t], 0);
             let out = hash_with_keys(k0, k1, &Bytes(buf.as_slice()));
-            debug!("got {:?}, expected {:?}", out, vec);
+            debug!("got {}, expected {}", out, vec);
             assert_eq!(vec, out);
 
             state_full.reset();
@@ -412,9 +412,6 @@ mod tests {
             let v = to_hex_str(&vecs[t]);
             debug!("{}: ({}) => inc={} full={}", t, v, i, f);
 
-            debug!("full state {:?}", state_full);
-            debug!("inc  state {:?}", state_inc);
-
             assert_eq!(f, i);
             assert_eq!(f, v);
 
diff --git a/src/libcollections/ringbuf.rs b/src/libcollections/ringbuf.rs
index 4d8e67f6ac8..1ae63d11fbe 100644
--- a/src/libcollections/ringbuf.rs
+++ b/src/libcollections/ringbuf.rs
@@ -551,21 +551,21 @@ mod tests {
         assert_eq!(d.len(), 3u);
         d.push(137);
         assert_eq!(d.len(), 4u);
-        debug!("{:?}", d.front());
+        debug!("{}", d.front());
         assert_eq!(*d.front().unwrap(), 42);
-        debug!("{:?}", d.back());
+        debug!("{}", d.back());
         assert_eq!(*d.back().unwrap(), 137);
         let mut i = d.pop_front();
-        debug!("{:?}", i);
+        debug!("{}", i);
         assert_eq!(i, Some(42));
         i = d.pop();
-        debug!("{:?}", i);
+        debug!("{}", i);
         assert_eq!(i, Some(137));
         i = d.pop();
-        debug!("{:?}", i);
+        debug!("{}", i);
         assert_eq!(i, Some(137));
         i = d.pop();
-        debug!("{:?}", i);
+        debug!("{}", i);
         assert_eq!(i, Some(17));
         assert_eq!(d.len(), 0u);
         d.push(3);
@@ -576,10 +576,10 @@ mod tests {
         assert_eq!(d.len(), 3u);
         d.push_front(1);
         assert_eq!(d.len(), 4u);
-        debug!("{:?}", d.get(0));
-        debug!("{:?}", d.get(1));
-        debug!("{:?}", d.get(2));
-        debug!("{:?}", d.get(3));
+        debug!("{}", d.get(0));
+        debug!("{}", d.get(1));
+        debug!("{}", d.get(2));
+        debug!("{}", d.get(3));
         assert_eq!(*d.get(0), 1);
         assert_eq!(*d.get(1), 2);
         assert_eq!(*d.get(2), 3);