diff --git a/components/script/textinput.rs b/components/script/textinput.rs
index 0ac002b9b9f..92fd76706f2 100644
--- a/components/script/textinput.rs
+++ b/components/script/textinput.rs
@@ -236,7 +236,7 @@ impl<T: ClipboardProvider> TextInput<T> {
     /// The length of the selected text in UTF-16 code units.
     fn selection_utf16_len(&self) -> usize {
         self.fold_selection_slices(0usize,
-            |len, slice| *len += slice.chars().map(char::len_utf16).sum())
+            |len, slice| *len += slice.chars().map(char::len_utf16).sum::<usize>())
     }
 
     /// Run the callback on a series of slices that, concatenated, make up the selected text.
diff --git a/rust-toolchain b/rust-toolchain
index 1ca562033e9..1b3072e1045 100644
--- a/rust-toolchain
+++ b/rust-toolchain
@@ -1 +1 @@
-nightly-2017-09-17
+nightly-2017-10-01