diff --git a/src/lvalue.rs b/src/lvalue.rs
index 2cce67689d72..e86c480aa0b6 100644
--- a/src/lvalue.rs
+++ b/src/lvalue.rs
@@ -1,6 +1,6 @@
 use rustc::hir::def_id::DefId;
 use rustc::mir;
-use rustc::ty::layout::Size;
+use rustc::ty::layout::{Size, Align};
 use rustc::ty::subst::Substs;
 use rustc::ty::{self, Ty};
 use rustc_data_structures::indexed_vec::Idx;
@@ -217,8 +217,7 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
                 let offset = match base_extra {
                     LvalueExtra::Vtable(tab) => {
                         let (_, align) = self.size_and_align_of_dst(base_ty, Value::ByValPair(PrimVal::Ptr(base_ptr), PrimVal::Ptr(tab)))?;
-                        // magical formula taken from rustc
-                        (offset.bytes() + (align - 1)) & (-(align as i64) as u64)
+                        offset.abi_align(Align::from_bytes(align, align).unwrap()).bytes()
                     }
                     _ => offset.bytes(),
                 };