diff --git a/src/buf/decode.rs b/src/buf/decode.rs
index 39dd6c0..2e6465d 100644
--- a/src/buf/decode.rs
+++ b/src/buf/decode.rs
@@ -5,13 +5,6 @@ use crate::{
 
 use super::*;
 
-#[derive(Debug)]
-pub enum ParseError {
-    IncompleteInput,
-    DuplicateKey(Pos),
-    Garbage(Pos),
-}
-
 pub fn decode(input: &[u8]) -> Result<(Buf<'_>, ITerm), ParseError> {
     let mut buf = Buf {
         bytes: input.into(),
@@ -62,7 +55,7 @@ impl<'a> Buf<'a> {
 
         let rest = self.take_whitespace(rest);
         if rest.start < raw.end {
-            return Err(ParseError::Garbage(rest.start));
+            return Err(ParseError::UnexpectedInput(rest.start as usize));
         }
 
         Ok(term)
@@ -181,7 +174,7 @@ impl<'a> Buf<'a> {
                     .zip(self.dicts[dict_start + 1..].iter())
                 {
                     if self.get_bytes(*k1) == self.get_bytes(*k2) {
-                        return Err(ParseError::DuplicateKey(k1.start));
+                        return Err(ParseError::DuplicateKey(String::from_utf8(self.get_bytes(*k1).to_vec()).unwrap()));
                     }
                 }
 
@@ -265,7 +258,7 @@ impl<'a> Buf<'a> {
         if raw.start >= raw.end {
             Err(ParseError::IncompleteInput)
         } else if self.bytes[raw.start as usize] != c {
-            Err(ParseError::Garbage(raw.start))
+            Err(ParseError::UnexpectedInput(raw.start as usize))
         } else {
             Ok(IRaw {
                 start: raw.start + 1,
@@ -294,7 +287,7 @@ impl<'a> Buf<'a> {
     #[inline]
     fn error_at(&self, raw: IRaw) -> ParseError {
         if raw.start < raw.end {
-            ParseError::Garbage(raw.start)
+            ParseError::UnexpectedInput(raw.start as usize)
         } else {
             ParseError::IncompleteInput
         }
diff --git a/src/buf/error.rs b/src/buf/error.rs
new file mode 100644
index 0000000..c3e06bf
--- /dev/null
+++ b/src/buf/error.rs
@@ -0,0 +1,39 @@
+use err_derive::Error;
+
+use super::*;
+
+#[derive(Debug, Error)]
+pub enum ParseError {
+    #[error(display = "Incomplete input")]
+    IncompleteInput,
+    #[error(display = "UnexpectedInput at position {}", _0)]
+    UnexpectedInput(usize),
+    #[error(display = "Duplicate dictionnary key: {}", _0)]
+    DuplicateKey(String),
+}
+
+#[derive(Debug, Error)]
+pub enum TermError {
+    #[error(display = "Invalid term index ({:?})", _0)]
+    InvalidIndex(ITerm),
+    #[error(display = "Wrong type, expected {}, got {}", _0, _1)]
+    WrongType(&'static str, &'static str),
+    #[error(display = "Wrong length, expected {}, got {}", _0, _1)]
+    WrongLength(usize, usize),
+    #[error(display = "Wrong dictionnary keys")]
+    WrongKeys,
+    #[error(display = "Term does not have a raw representation")]
+    NoRawRepresentation,
+}
+
+#[derive(Debug, Error)]
+pub enum ValueError {
+    #[error(display = "Invalid term index ({:?})", _0)]
+    InvalidIndex(ITerm),
+    #[error(display = "Duplicate dictionary key")]
+    DuplicateKey,
+    #[error(display = "Bad string (contains invalid characters)")]
+    BadString,
+    #[error(display = "Nested sequence")]
+    SeqInSeq,
+}
diff --git a/src/buf/mod.rs b/src/buf/mod.rs
index 24c4409..7f3ae26 100644
--- a/src/buf/mod.rs
+++ b/src/buf/mod.rs
@@ -1,9 +1,11 @@
 mod decode;
+mod error;
 
 use std::borrow::Cow;
 
 use crate::is_string_char;
 
+pub use error::*;
 pub use decode::*;
 
 pub(crate) const STR_INLINE_MAX: usize = 18;
@@ -51,23 +53,6 @@ pub struct Buf<'a> {
     terms: Vec<TTerm>,
 }
 
-#[derive(Debug)]
-pub enum TermError {
-    InvalidIndex(ITerm),
-    WrongType(&'static str, &'static str),
-    WrongLength(usize, usize),
-    WrongKeys,
-    NoRawRepresentation,
-}
-
-#[derive(Debug)]
-pub enum ValueError {
-    InvalidIndex(ITerm),
-    DuplicateKey,
-    BadString,
-    SeqInSeq,
-}
-
 impl<'a> Buf<'a> {
     pub fn new() -> Self {
         Self {
@@ -350,7 +335,11 @@ impl<'a> Buf<'a> {
             self.terms.truncate(terms_len);
         }
 
-        result
+        if let Err(ParseError::UnexpectedInput(pos)) = result {
+            Err(ParseError::UnexpectedInput(pos - bytes_len))
+        } else {
+            result
+        }
     }
 
     // ==== Internal ====