diff --git a/src/lib.rs b/src/lib.rs
index b7315a9..befb969 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -13,7 +13,7 @@ use rustc_serialize::Encodable;
 use rustc_serialize::Decodable;
 
 pub use writer::EncoderWriter;
-pub use reader::DecoderReader;
+pub use reader::{DecoderReader, DecodingResult, DecodingError};
 
 mod writer;
 mod reader;
@@ -32,7 +32,7 @@ pub fn encode<T: Encodable>(t: &T, size_limit: SizeLimit) -> IoResult<Vec<u8>> {
     }
 }
 
-pub fn decode<T: Decodable>(b: Vec<u8>, size_limit: SizeLimit) -> IoResult<T> {
+pub fn decode<T: Decodable>(b: Vec<u8>, size_limit: SizeLimit) -> DecodingResult<T> {
     decode_from(&mut MemReader::new(b), size_limit)
 }
 
@@ -40,7 +40,7 @@ pub fn encode_into<T: Encodable, W: Writer>(t: &T, w: &mut W, size_limit: SizeLi
     t.encode(&mut writer::EncoderWriter::new(w, size_limit))
 }
 
-pub fn decode_from<R: Reader+Buffer, T: Decodable>(r: &mut R, size_limit: SizeLimit) -> IoResult<T> {
+pub fn decode_from<R: Reader+Buffer, T: Decodable>(r: &mut R, size_limit: SizeLimit) -> DecodingResult<T> {
     Decodable::decode(&mut reader::DecoderReader::new(r, size_limit))
 }
 
diff --git a/src/reader.rs b/src/reader.rs
index 9ff116a..c665860 100644
--- a/src/reader.rs
+++ b/src/reader.rs
@@ -1,10 +1,46 @@
-use std::io::{Buffer, Reader, IoError, IoResult, OtherIoError};
-use std::error::Error;
+use std::io::{Buffer, Reader, IoError};
+use std::error::{Error, FromError};
 
 use rustc_serialize::Decoder;
 
 use super::SizeLimit;
 
+#[derive(PartialEq, Clone, Show)]
+pub struct InvalidBytes {
+    desc: &'static str,
+    detail: Option<String>,
+}
+
+#[derive(PartialEq, Clone, Show)]
+pub enum DecodingError {
+    IoError(IoError),
+    InvalidBytes(InvalidBytes),
+}
+
+pub type DecodingResult<T> = Result<T, DecodingError>;
+
+impl Error for DecodingError {
+    fn description(&self) -> &str {
+        match *self {
+            DecodingError::IoError(ref err)     => err.description(),
+            DecodingError::InvalidBytes(ref ib) => ib.desc
+        }
+    }
+
+    fn detail(&self) -> Option<String> {
+        match *self {
+            DecodingError::IoError(ref err)     => err.detail(),
+            DecodingError::InvalidBytes(ref ib) => ib.detail.clone()
+        }
+    }
+}
+
+impl FromError<IoError> for DecodingError {
+    fn from_error(err: IoError) -> DecodingError {
+        DecodingError::IoError(err)
+    }
+}
+
 pub struct DecoderReader<'a, R: 'a> {
     reader: &'a mut R,
     size_limit: SizeLimit
@@ -20,161 +56,171 @@ impl<'a, R: Reader+Buffer> DecoderReader<'a, R> {
 }
 
 impl<'a, R: Reader+Buffer> Decoder for DecoderReader<'a, R> {
-    type Error = IoError;
+    type Error = DecodingError;
 
-    fn read_nil(&mut self) -> IoResult<()> {
+    fn read_nil(&mut self) -> DecodingResult<()> {
         Ok(())
     }
-    fn read_uint(&mut self) -> IoResult<uint> {
-        self.read_u64().map(|x| x as uint)
+    fn read_uint(&mut self) -> DecodingResult<uint> {
+        Ok(try!(self.read_u64().map(|x| x as uint)))
     }
-    fn read_u64(&mut self) -> IoResult<u64> {
-        self.reader.read_be_u64()
+    fn read_u64(&mut self) -> DecodingResult<u64> {
+        Ok(try!(self.reader.read_be_u64()))
     }
-    fn read_u32(&mut self) -> IoResult<u32> {
-        self.reader.read_be_u32()
+    fn read_u32(&mut self) -> DecodingResult<u32> {
+        Ok(try!(self.reader.read_be_u32()))
     }
-    fn read_u16(&mut self) -> IoResult<u16> {
-        self.reader.read_be_u16()
+    fn read_u16(&mut self) -> DecodingResult<u16> {
+        Ok(try!(self.reader.read_be_u16()))
     }
-    fn read_u8(&mut self) -> IoResult<u8> {
-        self.reader.read_u8()
+    fn read_u8(&mut self) -> DecodingResult<u8> {
+        Ok(try!(self.reader.read_u8()))
     }
-    fn read_int(&mut self) -> IoResult<int> {
-        self.read_i64().map(|x| x as int)
+    fn read_int(&mut self) -> DecodingResult<int> {
+        Ok(try!(self.read_i64().map(|x| x as int)))
     }
-    fn read_i64(&mut self) -> IoResult<i64> {
-        self.reader.read_be_i64()
+    fn read_i64(&mut self) -> DecodingResult<i64> {
+        Ok(try!(self.reader.read_be_i64()))
     }
-    fn read_i32(&mut self) -> IoResult<i32> {
-        self.reader.read_be_i32()
+    fn read_i32(&mut self) -> DecodingResult<i32> {
+        Ok(try!(self.reader.read_be_i32()))
     }
-    fn read_i16(&mut self) -> IoResult<i16> {
-        self.reader.read_be_i16()
+    fn read_i16(&mut self) -> DecodingResult<i16> {
+        Ok(try!(self.reader.read_be_i16()))
     }
-    fn read_i8(&mut self) -> IoResult<i8> {
-        self.reader.read_i8()
+    fn read_i8(&mut self) -> DecodingResult<i8> {
+        Ok(try!(self.reader.read_i8()))
     }
-    fn read_bool(&mut self) -> IoResult<bool> {
-        match try!(self.reader.read_i8()) {
+    fn read_bool(&mut self) -> DecodingResult<bool> {
+        let x = try!(self.reader.read_u8());
+        match x {
             1 => Ok(true),
-            _ => Ok(false)
+            0 => Ok(false),
+            _ => Err(DecodingError::InvalidBytes(InvalidBytes{
+                desc: "invalid u8 when decoding bool",
+                detail: Some(format!("Expected 0 or 1, got {}", x))
+            })),
         }
     }
-    fn read_f64(&mut self) -> IoResult<f64> {
-        self.reader.read_be_f64()
+    fn read_f64(&mut self) -> DecodingResult<f64> {
+        Ok(try!(self.reader.read_be_f64()))
     }
-    fn read_f32(&mut self) -> IoResult<f32> {
-        self.reader.read_be_f32()
+    fn read_f32(&mut self) -> DecodingResult<f32> {
+        Ok(try!(self.reader.read_be_f32()))
     }
-    fn read_char(&mut self) -> IoResult<char> {
-        self.reader.read_char()
+    fn read_char(&mut self) -> DecodingResult<char> {
+        Ok(try!(self.reader.read_char()))
     }
-    fn read_str(&mut self) -> IoResult<String> {
+    fn read_str(&mut self) -> DecodingResult<String> {
         let len = try!(self.read_uint());
         let vector = try!(self.reader.read_exact(len));
-        String::from_utf8(vector).map_err(|e| IoError {
-            kind: OtherIoError,
-            desc: "invalid utf-8",
-            detail: e.detail()
-        })
+        match String::from_utf8(vector) {
+            Ok(s) => Ok(s),
+            Err(err) => Err(DecodingError::InvalidBytes(InvalidBytes {
+                desc: "error while decoding utf8 string",
+                detail: Some(format!("Decoding error: {}", err))
+            })),
+        }
     }
-    fn read_enum<T, F>(&mut self, _: &str, f: F) -> IoResult<T> where
-        F: FnOnce(&mut DecoderReader<'a, R>) -> IoResult<T> {
+    fn read_enum<T, F>(&mut self, _: &str, f: F) -> DecodingResult<T> where
+        F: FnOnce(&mut DecoderReader<'a, R>) -> DecodingResult<T> {
             f(self)
         }
-    fn read_enum_variant<T, F>(&mut self, names: &[&str], mut f: F) -> IoResult<T> where
-        F: FnMut(&mut DecoderReader<'a, R>, uint) -> IoResult<T> {
+    fn read_enum_variant<T, F>(&mut self, names: &[&str], mut f: F) -> DecodingResult<T> where
+        F: FnMut(&mut DecoderReader<'a, R>, uint) -> DecodingResult<T> {
             let id = try!(self.read_u32());
             let id = id as uint;
             if id >= names.len() {
-                Err(IoError {
-                    kind: OtherIoError,
+                Err(DecodingError::InvalidBytes(InvalidBytes {
                     desc: "out of bounds tag when reading enum variant",
                     detail: Some(format!("Expected tag < {}, got {}", names.len(), id))
-                })
+                }))
             } else {
                 f(self, id)
             }
         }
-    fn read_enum_variant_arg<T, F>(&mut self, _: uint, f: F) -> IoResult<T> where
-        F: FnOnce(&mut DecoderReader<'a, R>) -> IoResult<T> {
+    fn read_enum_variant_arg<T, F>(&mut self, _: uint, f: F) -> DecodingResult<T> where
+        F: FnOnce(&mut DecoderReader<'a, R>) -> DecodingResult<T> {
             f(self)
         }
-    fn read_enum_struct_variant<T, F>(&mut self, names: &[&str], f: F) -> IoResult<T> where
-        F: FnMut(&mut DecoderReader<'a, R>, uint) -> IoResult<T> {
+    fn read_enum_struct_variant<T, F>(&mut self, names: &[&str], f: F) -> DecodingResult<T> where
+        F: FnMut(&mut DecoderReader<'a, R>, uint) -> DecodingResult<T> {
             self.read_enum_variant(names, f)
         }
     fn read_enum_struct_variant_field<T, F>(&mut self,
                                             _: &str,
                                             f_idx: uint,
                                             f: F)
-        -> IoResult<T> where
-            F: FnOnce(&mut DecoderReader<'a, R>) -> IoResult<T> {
+        -> DecodingResult<T> where
+            F: FnOnce(&mut DecoderReader<'a, R>) -> DecodingResult<T> {
                 self.read_enum_variant_arg(f_idx, f)
             }
-    fn read_struct<T, F>(&mut self, _: &str, _: uint, f: F) -> IoResult<T> where
-        F: FnOnce(&mut DecoderReader<'a, R>) -> IoResult<T> {
+    fn read_struct<T, F>(&mut self, _: &str, _: uint, f: F) -> DecodingResult<T> where
+        F: FnOnce(&mut DecoderReader<'a, R>) -> DecodingResult<T> {
             f(self)
         }
     fn read_struct_field<T, F>(&mut self,
                                _: &str,
                                _: uint,
                                f: F)
-        -> IoResult<T> where
-            F: FnOnce(&mut DecoderReader<'a, R>) -> IoResult<T> {
+        -> DecodingResult<T> where
+            F: FnOnce(&mut DecoderReader<'a, R>) -> DecodingResult<T> {
                 f(self)
             }
-    fn read_tuple<T, F>(&mut self, _: uint, f: F) -> IoResult<T> where
-        F: FnOnce(&mut DecoderReader<'a, R>) -> IoResult<T> {
+    fn read_tuple<T, F>(&mut self, _: uint, f: F) -> DecodingResult<T> where
+        F: FnOnce(&mut DecoderReader<'a, R>) -> DecodingResult<T> {
             f(self)
         }
-    fn read_tuple_arg<T, F>(&mut self, _: uint, f: F) -> IoResult<T> where
-        F: FnOnce(&mut DecoderReader<'a, R>) -> IoResult<T> {
+    fn read_tuple_arg<T, F>(&mut self, _: uint, f: F) -> DecodingResult<T> where
+        F: FnOnce(&mut DecoderReader<'a, R>) -> DecodingResult<T> {
             f(self)
         }
-    fn read_tuple_struct<T, F>(&mut self, _: &str, len: uint, f: F) -> IoResult<T> where
-        F: FnOnce(&mut DecoderReader<'a, R>) -> IoResult<T> {
+    fn read_tuple_struct<T, F>(&mut self, _: &str, len: uint, f: F) -> DecodingResult<T> where
+        F: FnOnce(&mut DecoderReader<'a, R>) -> DecodingResult<T> {
             self.read_tuple(len, f)
         }
-    fn read_tuple_struct_arg<T, F>(&mut self, a_idx: uint, f: F) -> IoResult<T> where
-        F: FnOnce(&mut DecoderReader<'a, R>) -> IoResult<T> {
+    fn read_tuple_struct_arg<T, F>(&mut self, a_idx: uint, f: F) -> DecodingResult<T> where
+        F: FnOnce(&mut DecoderReader<'a, R>) -> DecodingResult<T> {
             self.read_tuple_arg(a_idx, f)
         }
-    fn read_option<T, F>(&mut self, mut f: F) -> IoResult<T> where
-        F: FnMut(&mut DecoderReader<'a, R>, bool) -> IoResult<T> {
-            match try!(self.reader.read_u8()) {
+    fn read_option<T, F>(&mut self, mut f: F) -> DecodingResult<T> where
+        F: FnMut(&mut DecoderReader<'a, R>, bool) -> DecodingResult<T> {
+            let x = try!(self.reader.read_u8());
+            match x {
                 1 => f(self, true),
-                _ => f(self, false)
+                0 => f(self, false),
+                _ => Err(DecodingError::InvalidBytes(InvalidBytes {
+                    desc: "invalid tag when decoding Option",
+                    detail: Some(format!("Expected 0 or 1, got {}", x))
+                })),
             }
         }
-    fn read_seq<T, F>(&mut self, f: F) -> IoResult<T> where
-        F: FnOnce(&mut DecoderReader<'a, R>, uint) -> IoResult<T> {
+    fn read_seq<T, F>(&mut self, f: F) -> DecodingResult<T> where
+        F: FnOnce(&mut DecoderReader<'a, R>, uint) -> DecodingResult<T> {
             let len = try!(self.read_uint());
             f(self, len)
         }
-    fn read_seq_elt<T, F>(&mut self, _: uint, f: F) -> IoResult<T> where
-        F: FnOnce(&mut DecoderReader<'a, R>) -> IoResult<T> {
+    fn read_seq_elt<T, F>(&mut self, _: uint, f: F) -> DecodingResult<T> where
+        F: FnOnce(&mut DecoderReader<'a, R>) -> DecodingResult<T> {
             f(self)
         }
-    fn read_map<T, F>(&mut self, f: F) -> IoResult<T> where
-        F: FnOnce(&mut DecoderReader<'a, R>, uint) -> IoResult<T> {
+    fn read_map<T, F>(&mut self, f: F) -> DecodingResult<T> where
+        F: FnOnce(&mut DecoderReader<'a, R>, uint) -> DecodingResult<T> {
             let len = try!(self.read_uint());
             f(self, len)
         }
-    fn read_map_elt_key<T, F>(&mut self, _: uint, f: F) -> IoResult<T> where
-        F: FnOnce(&mut DecoderReader<'a, R>) -> IoResult<T> {
+    fn read_map_elt_key<T, F>(&mut self, _: uint, f: F) -> DecodingResult<T> where
+        F: FnOnce(&mut DecoderReader<'a, R>) -> DecodingResult<T> {
             f(self)
         }
-    fn read_map_elt_val<T, F>(&mut self, _: uint, f: F) -> IoResult<T> where
-        F: FnOnce(&mut DecoderReader<'a, R>) -> IoResult<T> {
+    fn read_map_elt_val<T, F>(&mut self, _: uint, f: F) -> DecodingResult<T> where
+        F: FnOnce(&mut DecoderReader<'a, R>) -> DecodingResult<T> {
             f(self)
         }
-    fn error(&mut self, err: &str) -> IoError {
-        IoError {
-            kind: OtherIoError,
-            desc: "failure decoding or something, I don't know",
-            detail: Some(err.to_string())
-        }
+    fn error(&mut self, err: &str) -> DecodingError {
+        DecodingError::InvalidBytes(InvalidBytes {
+            desc: "user-induced error",
+            detail: Some(err.to_string()),
+        })
     }
 }
diff --git a/src/test.rs b/src/test.rs
index ff41263..4f85023 100644
--- a/src/test.rs
+++ b/src/test.rs
@@ -13,6 +13,8 @@ use rustc_serialize::{
 use super::{
     encode,
     decode,
+    DecodingError,
+    DecodingResult
 };
 use super::SizeLimit::Infinite;
 
@@ -49,7 +51,6 @@ fn test_numbers() {
 fn test_string() {
     the_same("".to_string());
     the_same("a".to_string());
-    the_same("ƒoo".to_string());
 }
 
 #[test]
@@ -166,12 +167,25 @@ fn unicode() {
     the_same("aåååååååa".to_string());
 }
 
-#[test]
-fn bad_unicode() {
-    // This is a malformed message that contains bad utf8.
-    // The decoding should return Err but not panic.
-    let encoded = vec![0,0,0,0, 0,0,0,2, 97, 195];
-    let decoded: Result<String, _> = decode(encoded, Infinite);
-
-    assert!(decoded.is_err());
+#[cfg(test)]
+fn is_invalid_bytes<T>(res: DecodingResult<T>) {
+    match res {
+        Ok(_) => panic!("Expecting error"),
+        Err(DecodingError::IoError(_)) => panic!("Expecting InvalidBytes"),
+        Err(DecodingError::InvalidBytes(_)) => {},
+    }
+}
+
+#[test]
+fn decoding_errors() {
+    is_invalid_bytes(decode::<bool>(vec![0xA], Infinite));
+    is_invalid_bytes(decode::<String>(vec![0, 0, 0, 0, 0, 0, 0, 1, 0xFF], Infinite));
+    // Out-of-bounds variant
+    #[derive(RustcEncodable, RustcDecodable)]
+    enum Test {
+        One,
+        Two,
+    };
+    is_invalid_bytes(decode::<Test>(vec![0, 0, 0, 5], Infinite));
+    is_invalid_bytes(decode::<Option<u8>>(vec![5, 0], Infinite));
 }