diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index 7d11dd2800fd4..590f4e46c1d2f 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -71,6 +71,8 @@
 #![feature(cfg_target_has_atomic)]
 #![feature(concat_idents)]
 #![feature(const_fn)]
+#![feature(const_if_match)]
+#![feature(const_panic)]
 #![feature(const_fn_union)]
 #![feature(const_generics)]
 #![feature(const_ptr_offset_from)]
diff --git a/src/libcore/ptr/const_ptr.rs b/src/libcore/ptr/const_ptr.rs
index e5297a0c1e094..fc3c02e1f066d 100644
--- a/src/libcore/ptr/const_ptr.rs
+++ b/src/libcore/ptr/const_ptr.rs
@@ -288,10 +288,7 @@ impl<T: ?Sized> *const T {
         T: Sized,
     {
         let pointee_size = mem::size_of::<T>();
-        let ok = 0 < pointee_size && pointee_size <= isize::max_value() as usize;
-        // assert that the pointee size is valid in a const eval compatible way
-        // FIXME: do this with a real assert at some point
-        [()][(!ok) as usize];
+        assert!(0 < pointee_size && pointee_size <= isize::max_value() as usize);
         intrinsics::ptr_offset_from(self, origin)
     }