diff --git a/src/librustc/mir/interpret/mod.rs b/src/librustc/mir/interpret/mod.rs
index 238ffad0ae24c..2821000ccad69 100644
--- a/src/librustc/mir/interpret/mod.rs
+++ b/src/librustc/mir/interpret/mod.rs
@@ -701,3 +701,131 @@ fn bit_index(bits: Size) -> (usize, usize) {
     assert_eq!(b as usize as u64, b);
     (a as usize, b as usize)
 }
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, RustcEncodable, RustcDecodable, Hash)]
+pub enum ScalarMaybeUndef<Tag=(), Id=AllocId> {
+    Scalar(Scalar<Tag, Id>),
+    Undef,
+}
+
+impl<Tag> From<Scalar<Tag>> for ScalarMaybeUndef<Tag> {
+    #[inline(always)]
+    fn from(s: Scalar<Tag>) -> Self {
+        ScalarMaybeUndef::Scalar(s)
+    }
+}
+
+impl<Tag> fmt::Display for ScalarMaybeUndef<Tag> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ScalarMaybeUndef::Undef => write!(f, "uninitialized bytes"),
+            ScalarMaybeUndef::Scalar(s) => write!(f, "{}", s),
+        }
+    }
+}
+
+impl<'tcx> ScalarMaybeUndef<()> {
+    #[inline]
+    pub fn with_default_tag<Tag>(self) -> ScalarMaybeUndef<Tag>
+        where Tag: Default
+    {
+        match self {
+            ScalarMaybeUndef::Scalar(s) => ScalarMaybeUndef::Scalar(s.with_default_tag()),
+            ScalarMaybeUndef::Undef => ScalarMaybeUndef::Undef,
+        }
+    }
+}
+
+impl<'tcx, Tag> ScalarMaybeUndef<Tag> {
+    #[inline]
+    pub fn erase_tag(self) -> ScalarMaybeUndef
+    {
+        match self {
+            ScalarMaybeUndef::Scalar(s) => ScalarMaybeUndef::Scalar(s.erase_tag()),
+            ScalarMaybeUndef::Undef => ScalarMaybeUndef::Undef,
+        }
+    }
+
+    #[inline]
+    pub fn not_undef(self) -> EvalResult<'static, Scalar<Tag>> {
+        match self {
+            ScalarMaybeUndef::Scalar(scalar) => Ok(scalar),
+            ScalarMaybeUndef::Undef => err!(ReadUndefBytes(Size::from_bytes(0))),
+        }
+    }
+
+    #[inline(always)]
+    pub fn to_ptr(self) -> EvalResult<'tcx, Pointer<Tag>> {
+        self.not_undef()?.to_ptr()
+    }
+
+    #[inline(always)]
+    pub fn to_bits(self, target_size: Size) -> EvalResult<'tcx, u128> {
+        self.not_undef()?.to_bits(target_size)
+    }
+
+    #[inline(always)]
+    pub fn to_bool(self) -> EvalResult<'tcx, bool> {
+        self.not_undef()?.to_bool()
+    }
+
+    #[inline(always)]
+    pub fn to_char(self) -> EvalResult<'tcx, char> {
+        self.not_undef()?.to_char()
+    }
+
+    #[inline(always)]
+    pub fn to_f32(self) -> EvalResult<'tcx, f32> {
+        self.not_undef()?.to_f32()
+    }
+
+    #[inline(always)]
+    pub fn to_f64(self) -> EvalResult<'tcx, f64> {
+        self.not_undef()?.to_f64()
+    }
+
+    #[inline(always)]
+    pub fn to_u8(self) -> EvalResult<'tcx, u8> {
+        self.not_undef()?.to_u8()
+    }
+
+    #[inline(always)]
+    pub fn to_u32(self) -> EvalResult<'tcx, u32> {
+        self.not_undef()?.to_u32()
+    }
+
+    #[inline(always)]
+    pub fn to_u64(self) -> EvalResult<'tcx, u64> {
+        self.not_undef()?.to_u64()
+    }
+
+    #[inline(always)]
+    pub fn to_usize(self, cx: &impl HasDataLayout) -> EvalResult<'tcx, u64> {
+        self.not_undef()?.to_usize(cx)
+    }
+
+    #[inline(always)]
+    pub fn to_i8(self) -> EvalResult<'tcx, i8> {
+        self.not_undef()?.to_i8()
+    }
+
+    #[inline(always)]
+    pub fn to_i32(self) -> EvalResult<'tcx, i32> {
+        self.not_undef()?.to_i32()
+    }
+
+    #[inline(always)]
+    pub fn to_i64(self) -> EvalResult<'tcx, i64> {
+        self.not_undef()?.to_i64()
+    }
+
+    #[inline(always)]
+    pub fn to_isize(self, cx: &impl HasDataLayout) -> EvalResult<'tcx, i64> {
+        self.not_undef()?.to_isize(cx)
+    }
+}
+
+impl_stable_hash_for!(enum ::mir::interpret::ScalarMaybeUndef {
+    Scalar(v),
+    Undef
+});
diff --git a/src/librustc_mir/interpret/operand.rs b/src/librustc_mir/interpret/operand.rs
index 83a2d14b7ca4c..76bf215316711 100644
--- a/src/librustc_mir/interpret/operand.rs
+++ b/src/librustc_mir/interpret/operand.rs
@@ -23,130 +23,7 @@ use rustc::mir::interpret::{
     EvalResult, EvalErrorKind
 };
 use super::{EvalContext, Machine, MemPlace, MPlaceTy, MemoryKind};
-
-#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, RustcEncodable, RustcDecodable, Hash)]
-pub enum ScalarMaybeUndef<Tag=(), Id=AllocId> {
-    Scalar(Scalar<Tag, Id>),
-    Undef,
-}
-
-impl<Tag> From<Scalar<Tag>> for ScalarMaybeUndef<Tag> {
-    #[inline(always)]
-    fn from(s: Scalar<Tag>) -> Self {
-        ScalarMaybeUndef::Scalar(s)
-    }
-}
-
-impl<Tag> fmt::Display for ScalarMaybeUndef<Tag> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            ScalarMaybeUndef::Undef => write!(f, "uninitialized bytes"),
-            ScalarMaybeUndef::Scalar(s) => write!(f, "{}", s),
-        }
-    }
-}
-
-impl<'tcx> ScalarMaybeUndef<()> {
-    #[inline]
-    pub fn with_default_tag<Tag>(self) -> ScalarMaybeUndef<Tag>
-        where Tag: Default
-    {
-        match self {
-            ScalarMaybeUndef::Scalar(s) => ScalarMaybeUndef::Scalar(s.with_default_tag()),
-            ScalarMaybeUndef::Undef => ScalarMaybeUndef::Undef,
-        }
-    }
-}
-
-impl<'tcx, Tag> ScalarMaybeUndef<Tag> {
-    #[inline]
-    pub fn erase_tag(self) -> ScalarMaybeUndef
-    {
-        match self {
-            ScalarMaybeUndef::Scalar(s) => ScalarMaybeUndef::Scalar(s.erase_tag()),
-            ScalarMaybeUndef::Undef => ScalarMaybeUndef::Undef,
-        }
-    }
-
-    #[inline]
-    pub fn not_undef(self) -> EvalResult<'static, Scalar<Tag>> {
-        match self {
-            ScalarMaybeUndef::Scalar(scalar) => Ok(scalar),
-            ScalarMaybeUndef::Undef => err!(ReadUndefBytes(Size::from_bytes(0))),
-        }
-    }
-
-    #[inline(always)]
-    pub fn to_ptr(self) -> EvalResult<'tcx, Pointer<Tag>> {
-        self.not_undef()?.to_ptr()
-    }
-
-    #[inline(always)]
-    pub fn to_bits(self, target_size: Size) -> EvalResult<'tcx, u128> {
-        self.not_undef()?.to_bits(target_size)
-    }
-
-    #[inline(always)]
-    pub fn to_bool(self) -> EvalResult<'tcx, bool> {
-        self.not_undef()?.to_bool()
-    }
-
-    #[inline(always)]
-    pub fn to_char(self) -> EvalResult<'tcx, char> {
-        self.not_undef()?.to_char()
-    }
-
-    #[inline(always)]
-    pub fn to_f32(self) -> EvalResult<'tcx, f32> {
-        self.not_undef()?.to_f32()
-    }
-
-    #[inline(always)]
-    pub fn to_f64(self) -> EvalResult<'tcx, f64> {
-        self.not_undef()?.to_f64()
-    }
-
-    #[inline(always)]
-    pub fn to_u8(self) -> EvalResult<'tcx, u8> {
-        self.not_undef()?.to_u8()
-    }
-
-    #[inline(always)]
-    pub fn to_u32(self) -> EvalResult<'tcx, u32> {
-        self.not_undef()?.to_u32()
-    }
-
-    #[inline(always)]
-    pub fn to_u64(self) -> EvalResult<'tcx, u64> {
-        self.not_undef()?.to_u64()
-    }
-
-    #[inline(always)]
-    pub fn to_usize(self, cx: &impl HasDataLayout) -> EvalResult<'tcx, u64> {
-        self.not_undef()?.to_usize(cx)
-    }
-
-    #[inline(always)]
-    pub fn to_i8(self) -> EvalResult<'tcx, i8> {
-        self.not_undef()?.to_i8()
-    }
-
-    #[inline(always)]
-    pub fn to_i32(self) -> EvalResult<'tcx, i32> {
-        self.not_undef()?.to_i32()
-    }
-
-    #[inline(always)]
-    pub fn to_i64(self) -> EvalResult<'tcx, i64> {
-        self.not_undef()?.to_i64()
-    }
-
-    #[inline(always)]
-    pub fn to_isize(self, cx: &impl HasDataLayout) -> EvalResult<'tcx, i64> {
-        self.not_undef()?.to_isize(cx)
-    }
-}
-
+pub use rustc::mir::interpret::ScalarMaybeUndef;
 
 /// A `Value` represents a single immediate self-contained Rust value.
 ///
diff --git a/src/librustc_mir/interpret/snapshot.rs b/src/librustc_mir/interpret/snapshot.rs
index 0926ddb596659..4b63335ad964c 100644
--- a/src/librustc_mir/interpret/snapshot.rs
+++ b/src/librustc_mir/interpret/snapshot.rs
@@ -195,11 +195,6 @@ impl<'a, Ctx> Snapshot<'a, Ctx> for Scalar
     }
 }
 
-impl_stable_hash_for!(enum ::interpret::ScalarMaybeUndef {
-    Scalar(v),
-    Undef
-});
-
 impl_snapshot_for!(enum ScalarMaybeUndef {
     Scalar(s),
     Undef,