diff --git a/src/fn_call.rs b/src/fn_call.rs
index 2b4e7b736628..272c27e40219 100644
--- a/src/fn_call.rs
+++ b/src/fn_call.rs
@@ -459,7 +459,7 @@ impl<'a, 'mir, 'tcx: 'mir + 'a> EvalContextExt<'tcx> for EvalContext<'a, 'mir, '
                             promoted: None,
                         };
                         let const_val = self.const_eval(cid)?;
-                        let value = const_val.val.unwrap_u64();
+                        let value = const_val.unwrap_usize(self.tcx.tcx);
                         if value == name {
                             result = Some(path_value);
                             break;
diff --git a/src/validation.rs b/src/validation.rs
index b274b4650157..deb1c5d5bc07 100644
--- a/src/validation.rs
+++ b/src/validation.rs
@@ -10,7 +10,7 @@ use rustc::infer::InferCtxt;
 use rustc::middle::region;
 use rustc::middle::const_val::ConstVal;
 use rustc_data_structures::indexed_vec::Idx;
-use rustc_mir::interpret::{HasMemory, eval_body};
+use rustc_mir::interpret::HasMemory;
 
 use super::{EvalContext, Place, PlaceExtra, ValTy};
 use rustc::mir::interpret::{DynamicLifetime, AccessKind, EvalErrorKind, Value, EvalError, EvalResult};
@@ -718,18 +718,17 @@ impl<'a, 'mir, 'tcx: 'mir + 'a> EvalContextExt<'tcx> for EvalContext<'a, 'mir, '
                     }
                 }
                 TyArray(elem_ty, len) => {
-                    let len_val = match len.val {
+                    let len = match len.val {
                         ConstVal::Unevaluated(def_id, substs) => {
-                            eval_body(self.tcx.tcx, GlobalId {
+                            self.tcx.const_eval(self.tcx.param_env(def_id).and(GlobalId {
                                 instance: Instance::new(def_id, substs),
                                 promoted: None,
-                            }, ty::ParamEnv::reveal_all())
-                                .ok_or_else(||EvalErrorKind::MachineError("<already reported>".to_string()))?
-                                .0
+                            }))
+                                .map_err(|_err|EvalErrorKind::MachineError("<already reported>".to_string()))?
                         }
-                        ConstVal::Value(val) => val,
+                        ConstVal::Value(_) => len,
                     };
-                    let len = ConstVal::Value(len_val).unwrap_u64();
+                    let len = len.unwrap_usize(self.tcx.tcx);
                     for i in 0..len {
                         let inner_place = self.place_index(query.place.1, query.ty, i as u64)?;
                         self.validate(