diff --git a/src/librustc/ich/impls_ty.rs b/src/librustc/ich/impls_ty.rs
index b2ad7e923b068..0ddc9211f9811 100644
--- a/src/librustc/ich/impls_ty.rs
+++ b/src/librustc/ich/impls_ty.rs
@@ -180,6 +180,7 @@ impl<'a> HashStable<StableHashingContext<'a>> for mir::interpret::Allocation {
             extra: _,
         } = self;
         bytes.hash_stable(hcx, hasher);
+        relocations.len().hash_stable(hcx, hasher);
         for reloc in relocations.iter() {
             reloc.hash_stable(hcx, hasher);
         }