diff --git a/compiler/rustc_data_structures/src/stable_hasher.rs b/compiler/rustc_data_structures/src/stable_hasher.rs
index 3ed1de1bc3c..1608009809f 100644
--- a/compiler/rustc_data_structures/src/stable_hasher.rs
+++ b/compiler/rustc_data_structures/src/stable_hasher.rs
@@ -107,7 +107,8 @@ fn write_u64(&mut self, i: u64) {
 
     #[inline]
     fn write_u128(&mut self, i: u128) {
-        self.state.write(&i.to_le_bytes());
+        self.write_u64(i as u64);
+        self.write_u64((i >> 64) as u64);
     }
 
     #[inline]