diff --git a/src/lib.rs b/src/lib.rs
index fdf08c001a3f..c075589e99c4 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -11,6 +11,7 @@
 #![feature(rustc_private)]
 #![feature(custom_attribute)]
 #![feature(slice_splits)]
+#![feature(slice_patterns)]
 #![feature(catch_panic)]
 #![allow(unused_attributes)]
 
diff --git a/src/types.rs b/src/types.rs
index 69ee7193ab23..2b757671a139 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -484,22 +484,16 @@ impl Rewrite for ast::Ty {
                 ty.rewrite(context, budget, offset + 1).map(|ty_str| format!("({})", ty_str))
             }
             ast::TyTup(ref tup_ret) => {
-                let inner = try_opt!(tup_ret.iter()
-                                            .map(|item| item.rewrite(context, width, offset))
-                                            .fold(Some("".to_owned()),
-                                                  |sum, x| {
-                                                      match (sum, x) {
-                                                          (Some(sum), Some(x)) => {
-                                                              if sum == "" {
-                                                                  // First item.
-                                                                  Some(x)
-                                                              } else {
-                                                                  Some(sum + ", " + &x)
-                                                              }
-                                                          }
-                                                          _ => None,
-                                                      }
-                                                  }));
+                let inner = if let [ref item] = &**tup_ret {
+                    try_opt!(item.rewrite(context, width, offset)) + ","
+                } else {
+                    let rewrites: Option<Vec<_>>;
+                    rewrites = tup_ret.iter()
+                                      .map(|item| item.rewrite(context, width, offset))
+                                      .collect();
+
+                    try_opt!(rewrites).join(", ")
+                };
 
                 let ret = format!("({})", inner);
                 wrap_str(ret, context.config.max_width, width, offset)
diff --git a/tests/target/fn_once.rs b/tests/target/fn_once.rs
new file mode 100644
index 000000000000..42b8f98e78ab
--- /dev/null
+++ b/tests/target/fn_once.rs
@@ -0,0 +1,8 @@
+struct Add(usize);
+
+impl FnOnce<(usize,)> for Add {
+    type Output = Add;
+    extern "rust-call" fn call_once(self, to: (usize,)) -> Add {
+        Add(self.0 + to.0)
+    }
+}