diff --git a/src/interpreter/terminator/intrinsics.rs b/src/interpreter/terminator/intrinsics.rs
index 236bb5ca00b..49cef471dab 100644
--- a/src/interpreter/terminator/intrinsics.rs
+++ b/src/interpreter/terminator/intrinsics.rs
@@ -352,7 +352,7 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
                     }
                 }
                 ty::TyTrait(..) => {
-                    let vtable = value.expect_vtable(&self.memory)?;
+                    let (_, vtable) = value.expect_ptr_vtable_pair(&self.memory)?;
                     // the second entry in the vtable is the dynamic size of the object.
                     let size = self.memory.read_usize(vtable.offset(pointer_size as isize))?;
                     let align = self.memory.read_usize(vtable.offset(pointer_size as isize * 2))?;
diff --git a/src/interpreter/terminator/mod.rs b/src/interpreter/terminator/mod.rs
index 132aa101f87..1555f22efb2 100644
--- a/src/interpreter/terminator/mod.rs
+++ b/src/interpreter/terminator/mod.rs
@@ -452,7 +452,8 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
             traits::VtableObject(ref data) => {
                 let idx = self.tcx.get_vtable_index_of_object_method(data, def_id);
                 if let Some(&mut(ref mut first_arg, ref mut first_ty)) = args.get_mut(0) {
-                    let vtable = first_arg.expect_vtable(&self.memory)?;
+                    let (self_ptr, vtable) = first_arg.expect_ptr_vtable_pair(&self.memory)?;
+                    *first_arg = Value::ByVal(PrimVal::Ptr(self_ptr));
                     let idx = idx + 3;
                     let offset = idx * self.memory.pointer_size();
                     let fn_ptr = self.memory.read_ptr(vtable.offset(offset as isize))?;
diff --git a/src/interpreter/value.rs b/src/interpreter/value.rs
index 178dbac8401..b89210c065d 100644
--- a/src/interpreter/value.rs
+++ b/src/interpreter/value.rs
@@ -29,12 +29,19 @@ impl<'a, 'tcx: 'a> Value {
         }
     }
 
-    pub(super) fn expect_vtable(&self, mem: &Memory<'a, 'tcx>) -> EvalResult<'tcx, Pointer> {
+    pub(super) fn expect_ptr_vtable_pair(
+        &self,
+        mem: &Memory<'a, 'tcx>
+    ) -> EvalResult<'tcx, (Pointer, Pointer)> {
         use self::Value::*;
         match *self {
-            ByRef(ptr) => mem.read_ptr(ptr.offset(mem.pointer_size() as isize)),
-            ByValPair(_, PrimVal::Ptr(vtable)) => Ok(vtable),
-            _ => unimplemented!(),
+            ByRef(ptr) => {
+                let ptr = mem.read_ptr(ptr)?;
+                let vtable = mem.read_ptr(ptr.offset(mem.pointer_size() as isize))?;
+                Ok((ptr, vtable))
+            }
+            ByValPair(PrimVal::Ptr(ptr), PrimVal::Ptr(vtable)) => Ok((ptr, vtable)),
+            _ => bug!("expected ptr and vtable, got {:?}", self),
         }
     }