diff --git a/src/librustc_const_eval/eval.rs b/src/librustc_const_eval/eval.rs
index 4fd4daf09980..1bd9b37b644b 100644
--- a/src/librustc_const_eval/eval.rs
+++ b/src/librustc_const_eval/eval.rs
@@ -408,6 +408,7 @@ pub enum ErrKind {
     TypeMismatch(String, ConstInt),
     BadType(ConstVal),
     ErroneousReferencedConstant(Box<ConstEvalErr>),
+    BadCharValue,
 }
 
 impl From<ConstMathErr> for ErrKind {
@@ -468,6 +469,7 @@ impl ConstEvalErr {
             },
             BadType(ref i) => format!("value of wrong type: {:?}", i).into_cow(),
             ErroneousReferencedConstant(_) => "could not evaluate referenced constant".into_cow(),
+            BadCharValue => "invalid numeric value for char".into_cow(),
         }
     }
 }
@@ -1075,23 +1077,19 @@ fn cast_const_int<'tcx>(tcx: &TyCtxt<'tcx>, val: ConstInt, ty: ty::Ty) -> CastRe
                 Err(_) => Ok(Integral(Usize(ConstUsize::Us32(v as u32)))),
             }
         },
-        ty::TyFloat(ast::FloatTy::F64) if val.is_negative() => {
-            // FIXME: this could probably be prettier
-            // there's no easy way to turn an `Infer` into a f64
-            let val = (-val).map_err(Math)?;
-            let val = val.to_u64().unwrap() as f64;
-            let val = -val;
-            Ok(Float(val))
+        ty::TyFloat(ast::FloatTy::F64) => match val.erase_type() {
+            Infer(u) => Ok(Float(u as f64)),
+            InferSigned(i) => Ok(Float(i as f64)),
+            _ => unreachable!(),
         },
-        ty::TyFloat(ast::FloatTy::F64) => Ok(Float(val.to_u64().unwrap() as f64)),
-        ty::TyFloat(ast::FloatTy::F32) if val.is_negative() => {
-            let val = (-val).map_err(Math)?;
-            let val = val.to_u64().unwrap() as f32;
-            let val = -val;
-            Ok(Float(val as f64))
+        ty::TyFloat(ast::FloatTy::F32) => match val.erase_type() {
+            Infer(u) => Ok(Float(u as f32 as f64)),
+            InferSigned(i) => Ok(Float(i as f32 as f64)),
+            _ => unreachable!(),
         },
-        ty::TyFloat(ast::FloatTy::F32) => Ok(Float(val.to_u64().unwrap() as f32 as f64)),
         ty::TyRawPtr(_) => Err(ErrKind::UnimplementedConstVal("casting an address to a raw ptr")),
+        ty::TyChar if v as u32 as u64 == v => ::std::char::from_u32(v as u32).map(Char)
+                                                                             .ok_or(BadCharValue),
         _ => Err(CannotCast),
     }
 }
diff --git a/src/test/run-pass/const-err.rs b/src/test/run-pass/const-err.rs
new file mode 100644
index 000000000000..8d7ac4f54c13
--- /dev/null
+++ b/src/test/run-pass/const-err.rs
@@ -0,0 +1,19 @@
+// Copyright 2015 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.
+
+// check for const_err regressions
+
+#![deny(const_err)]
+
+
+fn main() {
+    let _ = ((-1 as i8) << 8 - 1) as f32;
+    let _ = 0u8 as char;
+}