diff --git a/src/librustc/middle/const_eval.rs b/src/librustc/middle/const_eval.rs
index ad0040608ece8..c5fe6cdade6de 100644
--- a/src/librustc/middle/const_eval.rs
+++ b/src/librustc/middle/const_eval.rs
@@ -322,10 +322,9 @@ pub fn const_expr_to_pat(tcx: &ty::ctxt, expr: &Expr) -> P<Pat> {
 
         ExprCall(ref callee, ref args) => {
             let def = tcx.def_map.borrow().get_copy(&callee.id);
-            match tcx.def_map.borrow_mut().entry(expr.id) {
-              Vacant(entry) => { entry.set(def); }
-              _ => {}
-            };
+            if let Vacant(entry) = tcx.def_map.borrow_mut().entry(expr.id) {
+                entry.set(def);
+            }
             let path = match def {
                 def::DefStruct(def_id) => def_to_path(tcx, def_id),
                 def::DefVariant(_, variant_did, _) => def_to_path(tcx, variant_did),
@@ -560,7 +559,7 @@ pub fn eval_const_expr_partial(tcx: &ty::ctxt, e: &Expr) -> Result<const_val, St
               None => Err("non-constant path in constant expr".to_string())
           }
       }
-      ExprLit(ref lit) => Ok(lit_to_const(&**lit)),
+      ExprLit(ref lit) => Ok(lit_to_const(tcx, e.id, &**lit)),
       ExprParen(ref e)     => eval_const_expr_partial(tcx, &**e),
       ExprBlock(ref block) => {
         match block.expr {
@@ -572,25 +571,28 @@ pub fn eval_const_expr_partial(tcx: &ty::ctxt, e: &Expr) -> Result<const_val, St
     }
 }
 
-pub fn lit_to_const(lit: &Lit) -> const_val {
+pub fn lit_to_const(tcx: &ty::ctxt, id: ast::NodeId, lit: &Lit) -> const_val {
+    let t = ty::try_node_id_to_type(tcx, id);
     match lit.node {
-        LitStr(ref s, _) => const_str((*s).clone()),
-        LitBinary(ref data) => {
-            const_binary(Rc::new(data.iter().map(|x| *x).collect()))
-        }
-        LitByte(n) => const_uint(n as u64),
-        LitChar(n) => const_uint(n as u64),
-        LitInt(n, ast::SignedIntLit(_, ast::Plus)) |
-        LitInt(n, ast::UnsuffixedIntLit(ast::Plus)) => const_int(n as i64),
-        LitInt(n, ast::SignedIntLit(_, ast::Minus)) |
-        LitInt(n, ast::UnsuffixedIntLit(ast::Minus)) => const_int(-(n as i64)),
-        LitInt(n, ast::UnsignedIntLit(_)) => const_uint(n),
-        LitFloat(ref n, _) |
-        LitFloatUnsuffixed(ref n) => {
+        LitNil =>
+            const_nil,
+        LitBool(b) =>
+            const_bool(b),
+        LitByte(n) =>
+            const_uint(n as u64),
+        LitInt(n, _) => if t.into_iter().any(ty::type_is_signed) {
+            const_int(n as i64)
+        } else {
+            const_uint(n as u64)
+        },
+        LitChar(n) =>
+            const_uint(n as u64),
+        LitBinary(ref data) =>
+            const_binary(Rc::new(data.iter().map(|x| *x).collect())),
+        LitStr(ref s, _) =>
+            const_str((*s).clone()),
+        LitFloat(ref n, _) | LitFloatUnsuffixed(ref n) =>
             const_float(from_str::<f64>(n.get()).unwrap() as f64)
-        }
-        LitNil => const_nil,
-        LitBool(b) => const_bool(b)
     }
 }
 
diff --git a/src/librustc/middle/ty.rs b/src/librustc/middle/ty.rs
index b9af31665a113..97f28c8e9c312 100644
--- a/src/librustc/middle/ty.rs
+++ b/src/librustc/middle/ty.rs
@@ -3208,13 +3208,6 @@ pub fn node_id_to_type(cx: &ctxt, id: ast::NodeId) -> t {
     }
 }
 
-pub fn node_id_to_type_opt(cx: &ctxt, id: ast::NodeId) -> Option<t> {
-    match cx.node_types.borrow().find(&(id as uint)) {
-       Some(&t) => Some(t),
-       None => None
-    }
-}
-
 pub fn node_id_item_substs(cx: &ctxt, id: ast::NodeId) -> ItemSubsts {
     match cx.item_substs.borrow().find(&id) {
       None => ItemSubsts::empty(),
@@ -3338,7 +3331,7 @@ pub fn expr_ty(cx: &ctxt, expr: &ast::Expr) -> t {
 }
 
 pub fn expr_ty_opt(cx: &ctxt, expr: &ast::Expr) -> Option<t> {
-    return node_id_to_type_opt(cx, expr.id);
+    return try_node_id_to_type(cx, expr.id)
 }
 
 pub fn expr_ty_adjusted(cx: &ctxt, expr: &ast::Expr) -> t {
diff --git a/src/test/run-pass/issue-16745.rs b/src/test/run-pass/issue-16745.rs
new file mode 100644
index 0000000000000..862e859233376
--- /dev/null
+++ b/src/test/run-pass/issue-16745.rs
@@ -0,0 +1,26 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn is_whitespace(b: u8) -> bool {
+    match b {
+        b' '  => true,
+        b'\t' => true,
+        b'\n' => true,
+        0x0B  => true,
+        0x0C  => true,
+        b'\r' => true,
+        _     => false,
+    }
+}
+
+fn main() {
+    assert!(is_whitespace('\n' as u8));
+    assert!(!is_whitespace('f' as u8));
+}
diff --git a/src/test/run-pass/issue-17631.rs b/src/test/run-pass/issue-17631.rs
new file mode 100644
index 0000000000000..cff440d86d8ff
--- /dev/null
+++ b/src/test/run-pass/issue-17631.rs
@@ -0,0 +1,19 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub fn main() {
+    let (a, b) = (1u8, 2u8);
+
+    assert_eq!(match (a, b) {
+        (0x1b, 0x01) => 1u,
+        (_, 0x05u8) => 2u,
+        _ => 5u
+    }, 5u);
+}