diff --git a/src/librustc/mir/mod.rs b/src/librustc/mir/mod.rs
index b909269e153..a68a6acab3f 100644
--- a/src/librustc/mir/mod.rs
+++ b/src/librustc/mir/mod.rs
@@ -402,9 +402,11 @@ pub enum BorrowKind {
 ///////////////////////////////////////////////////////////////////////////
 // Variables and temps
 
-newtype_index!(Local, "_");
-
-pub const RETURN_POINTER: Local = Local(0);
+newtype_index!(Local,
+    const {
+        DESCRIPTION = "_",
+        RETURN_POINTER = 0,
+    });
 
 /// Classifies locals into categories. See `Mir::local_kind`.
 #[derive(PartialEq, Eq, Debug)]
@@ -538,7 +540,7 @@ pub struct UpvarDecl {
 ///////////////////////////////////////////////////////////////////////////
 // BasicBlock
 
-newtype_index!(BasicBlock, "bb");
+newtype_index!(BasicBlock, const { DESCRIPTION = "bb" });
 
 ///////////////////////////////////////////////////////////////////////////
 // BasicBlockData and Terminator
@@ -1118,7 +1120,7 @@ pub type LvalueProjection<'tcx> = Projection<'tcx, Lvalue<'tcx>, Local, Ty<'tcx>
 /// and the index is a local.
 pub type LvalueElem<'tcx> = ProjectionElem<'tcx, Local, Ty<'tcx>>;
 
-newtype_index!(Field, "field");
+newtype_index!(Field, const { DESCRIPTION = "field" });
 
 impl<'tcx> Lvalue<'tcx> {
     pub fn field(self, f: Field, ty: Ty<'tcx>) -> Lvalue<'tcx> {
@@ -1183,8 +1185,11 @@ impl<'tcx> Debug for Lvalue<'tcx> {
 ///////////////////////////////////////////////////////////////////////////
 // Scopes
 
-newtype_index!(VisibilityScope, "scope");
-pub const ARGUMENT_VISIBILITY_SCOPE : VisibilityScope = VisibilityScope(0);
+newtype_index!(VisibilityScope,
+    const {
+        DESCRIPTION = "scope",
+        ARGUMENT_VISIBILITY_SCOPE = 0,
+    });
 
 #[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
 pub struct VisibilityScopeData {
@@ -1509,7 +1514,7 @@ pub struct Constant<'tcx> {
     pub literal: Literal<'tcx>,
 }
 
-newtype_index!(Promoted, "promoted");
+newtype_index!(Promoted, const { DESCRIPTION = "promoted" });
 
 #[derive(Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 pub enum Literal<'tcx> {
diff --git a/src/librustc_data_structures/indexed_vec.rs b/src/librustc_data_structures/indexed_vec.rs
index 4b7f55eba06..0973bfd2429 100644
--- a/src/librustc_data_structures/indexed_vec.rs
+++ b/src/librustc_data_structures/indexed_vec.rs
@@ -40,39 +40,86 @@ impl Idx for u32 {
 
 #[macro_export]
 macro_rules! newtype_index {
-    ($name:ident) => (
-        newtype_index!($name, unsafe { ::std::intrinsics::type_name::<$name>() });
-    );
+    // ---- private rules ----
 
-    ($name:ident, $debug_name:expr) => (
+    // Base case, user-defined constants (if any) have already been defined
+    (@type[$type:ident] @max[$max:expr] @descr[$descr:expr]) => (
         #[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord,
-         RustcEncodable, RustcDecodable)]
-        pub struct $name(u32);
+            RustcEncodable, RustcDecodable)]
+        pub struct $type(u32);
 
-        impl $name {
-            // HACK use for constants
-            #[allow(unused)]
-            const fn const_new(x: u32) -> Self {
-                $name(x)
-            }
-        }
-
-        impl Idx for $name {
+        impl Idx for $type {
             fn new(value: usize) -> Self {
-                assert!(value < (::std::u32::MAX) as usize);
-                $name(value as u32)
+                assert!(value < ($max) as usize);
+                $type(value as u32)
             }
             fn index(self) -> usize {
                 self.0 as usize
             }
         }
 
-        impl ::std::fmt::Debug for $name {
+        impl ::std::fmt::Debug for $type {
             fn fmt(&self, fmt: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
-                write!(fmt, "{}{}", $debug_name, self.0)
+                write!(fmt, "{}{}", $descr, self.0)
             }
         }
-    )
+    );
+
+    // Replace existing default for max (as final param)
+    (@type[$type:ident] @max[$_max:expr] @descr[$descr:expr] MAX = $max:expr) => (
+        newtype_index!(@type[$type] @max[$max] @descr[$descr]);
+    );
+
+    // Replace existing default for max
+    (@type[$type:ident] @max[$_max:expr] @descr[$descr:expr] MAX = $max:expr, $($idents:ident = $constants:expr),*) => (
+        newtype_index!(@type[$type] @max[$max] @descr[$descr]);
+    );
+
+    // Replace existing default for description (as final param)
+    (@type[$type:ident] @max[$max:expr] @descr[$_descr:expr] DESCRIPTION = $descr:expr) => (
+        newtype_index!(@type[$type] @max[$max] @descr[$descr]);
+    );
+
+    // Replace existing default for description
+    (@type[$type:ident] @max[$max:expr] @descr[$_descr:expr] DESCRIPTION = $descr:expr, $($idents:ident = $constants:expr),*) => (
+        newtype_index!(@type[$type] @max[$max] @descr[$descr] $($idents = $constants),*);
+    );
+
+    // Assign a user-defined constant (as final param)
+    (@type[$type:ident] @max[$max:expr] @descr[$descr:expr] $name:ident = $constant:expr) => (
+        pub const $name: $type = $type($constant);
+        newtype_index!(@type[$type] @max[$max] @descr[$descr]);
+    );
+
+    // Assign a user-defined constant
+    (@type[$type:ident] @max[$max:expr] @descr[$descr:expr] $name:ident = $constant:expr, $($idents:ident = $constants:expr),*) => (
+        pub const $name: $type = $type($constant);
+        newtype_index!(@type[$type] @max[$max] @descr[$descr] $($idents = $constants),*);
+    );
+
+    // ---- public rules ----
+
+    // Use default constants
+    ($name:ident) => (
+        newtype_index!(
+            @type[$name]
+            @max[::std::u32::MAX]
+            @descr[unsafe {::std::intrinsics::type_name::<$name>() }]);
+    );
+
+    // Define any constants
+    ($name:ident, const { $($idents:ident = $constants:expr,)+ }) => (
+        newtype_index!(
+            @type[$name]
+            @max[::std::u32::MAX]
+            @descr[unsafe {::std::intrinsics::type_name::<$name>() }]
+            $($idents = $constants),+);
+    );
+
+    // Rewrite missing trailing comma in const to version with trailing comma
+    ($name:ident, const { $($idents:ident = $constants:expr),+ }) => (
+        newtype_index!($name, const { $($idents = $constants,)+ });
+    );
 }
 
 #[derive(Clone, PartialEq, Eq)]