diff --git a/src/Cargo.lock b/src/Cargo.lock
index b4455a34e49..6acdc8102a7 100644
--- a/src/Cargo.lock
+++ b/src/Cargo.lock
@@ -330,6 +330,7 @@ name = "rustc_data_structures"
 version = "0.0.0"
 dependencies = [
  "log 0.0.0",
+ "rustc_i128 0.0.0",
  "serialize 0.0.0",
 ]
 
diff --git a/src/librustc_data_structures/Cargo.toml b/src/librustc_data_structures/Cargo.toml
index e2e16059d98..bb610374810 100644
--- a/src/librustc_data_structures/Cargo.toml
+++ b/src/librustc_data_structures/Cargo.toml
@@ -11,3 +11,4 @@ crate-type = ["dylib"]
 [dependencies]
 log = { path = "../liblog" }
 serialize = { path = "../libserialize" }
+rustc_i128 = { path = "../librustc_i128" }
diff --git a/src/librustc_data_structures/lib.rs b/src/librustc_data_structures/lib.rs
index 86f244d65dd..d3ec674daed 100644
--- a/src/librustc_data_structures/lib.rs
+++ b/src/librustc_data_structures/lib.rs
@@ -44,6 +44,8 @@
 #[cfg(unix)]
 extern crate libc;
 
+extern crate rustc_i128;
+
 pub use rustc_serialize::hex::ToHex;
 
 pub mod array_vec;
diff --git a/src/librustc_data_structures/stable_hasher.rs b/src/librustc_data_structures/stable_hasher.rs
index ed97c3dde5e..87048eff5b7 100644
--- a/src/librustc_data_structures/stable_hasher.rs
+++ b/src/librustc_data_structures/stable_hasher.rs
@@ -13,13 +13,14 @@
 use std::mem;
 use blake2b::Blake2bHasher;
 use rustc_serialize::leb128;
+use rustc_i128::{u128,i128};
 
 fn write_unsigned_leb128_to_buf(buf: &mut [u8; 16], value: u64) -> usize {
-    leb128::write_unsigned_leb128_to(value, |i, v| buf[i] = v)
+    leb128::write_unsigned_leb128_to(value as u128, |i, v| buf[i] = v)
 }
 
 fn write_signed_leb128_to_buf(buf: &mut [u8; 16], value: i64) -> usize {
-    leb128::write_signed_leb128_to(value, |i, v| buf[i] = v)
+    leb128::write_signed_leb128_to(value as i128, |i, v| buf[i] = v)
 }
 
 /// When hashing something that ends up affecting properties like symbol names. We
diff --git a/src/libserialize/leb128.rs b/src/libserialize/leb128.rs
index 55ae7ae10f4..392f332d508 100644
--- a/src/libserialize/leb128.rs
+++ b/src/libserialize/leb128.rs
@@ -26,7 +26,7 @@ fn write_to_vec(vec: &mut Vec<u8>, position: usize, byte: u8) {
 /// The callback `write` is called once for each position
 /// that is to be written to with the byte to be encoded
 /// at that position.
-pub fn write_unsigned_leb128_to<W>(mut value: u64, mut write: W) -> usize
+pub fn write_unsigned_leb128_to<W>(mut value: u128, mut write: W) -> usize
     where W: FnMut(usize, u8)
 {
     let mut position = 0;
@@ -48,7 +48,7 @@ pub fn write_unsigned_leb128_to<W>(mut value: u64, mut write: W) -> usize
     position
 }
 
-pub fn write_unsigned_leb128(out: &mut Vec<u8>, start_position: usize, value: u64) -> usize {
+pub fn write_unsigned_leb128(out: &mut Vec<u8>, start_position: usize, value: u128) -> usize {
     write_unsigned_leb128_to(value, |i, v| write_to_vec(out, start_position+i, v))
 }