diff --git a/src/bench_enum.rs b/src/bench_enum.rs
index c5f75a46..815bb30d 100644
--- a/src/bench_enum.rs
+++ b/src/bench_enum.rs
@@ -231,27 +231,27 @@ mod deserializer {
 
     impl de::Deserializer<Error> for AnimalDeserializer {
         #[inline]
-        fn end_of_stream_error(&self) -> Error {
+        fn end_of_stream_error(&mut self) -> Error {
             EndOfStream
         }
 
         #[inline]
-        fn syntax_error(&self, _token: de::Token, _expected: &[de::TokenKind]) -> Error {
+        fn syntax_error(&mut self, _token: de::Token, _expected: &[de::TokenKind]) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn missing_field_error(&self, _field: &'static str) -> Error {
+        fn missing_field_error(&mut self, _field: &'static str) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn unexpected_name_error(&self, _token: de::Token) -> Error {
+        fn unexpected_name_error(&mut self, _token: de::Token) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn conversion_error(&self, _token: de::Token) -> Error {
+        fn conversion_error(&mut self, _token: de::Token) -> Error {
             SyntaxError
         }
     }
diff --git a/src/bench_map.rs b/src/bench_map.rs
index b23fe109..0faabcde 100644
--- a/src/bench_map.rs
+++ b/src/bench_map.rs
@@ -227,27 +227,27 @@ mod deserializer {
 
     impl de::Deserializer<Error> for IntDeserializer {
         #[inline]
-        fn end_of_stream_error(&self) -> Error {
+        fn end_of_stream_error(&mut self) -> Error {
             EndOfStream
         }
 
         #[inline]
-        fn syntax_error(&self, _token: de::Token, _expected: &[de::TokenKind]) -> Error {
+        fn syntax_error(&mut self, _token: de::Token, _expected: &[de::TokenKind]) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn missing_field_error(&self, _field: &'static str) -> Error {
+        fn missing_field_error(&mut self, _field: &'static str) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn unexpected_name_error(&self, _token: de::Token) -> Error {
+        fn unexpected_name_error(&mut self, _token: de::Token) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn conversion_error(&self, _token: de::Token) -> Error {
+        fn conversion_error(&mut self, _token: de::Token) -> Error {
             SyntaxError
         }
     }
diff --git a/src/bench_struct.rs b/src/bench_struct.rs
index 9e5e4591..dba8d7f7 100644
--- a/src/bench_struct.rs
+++ b/src/bench_struct.rs
@@ -351,27 +351,27 @@ mod deserializer {
 
     impl de::Deserializer<Error> for OuterDeserializer {
         #[inline]
-        fn end_of_stream_error(&self) -> Error {
+        fn end_of_stream_error(&mut self) -> Error {
             EndOfStream
         }
 
         #[inline]
-        fn syntax_error(&self, _token: de::Token, _expected: &[de::TokenKind]) -> Error {
+        fn syntax_error(&mut self, _token: de::Token, _expected: &[de::TokenKind]) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn missing_field_error(&self, _field: &'static str) -> Error {
+        fn missing_field_error(&mut self, _field: &'static str) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn unexpected_name_error(&self, _token: de::Token) -> Error {
+        fn unexpected_name_error(&mut self, _token: de::Token) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn conversion_error(&self, _token: de::Token) -> Error {
+        fn conversion_error(&mut self, _token: de::Token) -> Error {
             SyntaxError
         }
     }
diff --git a/src/bench_vec.rs b/src/bench_vec.rs
index 6b4c3691..3ba5201f 100644
--- a/src/bench_vec.rs
+++ b/src/bench_vec.rs
@@ -295,27 +295,27 @@ mod deserializer {
 
     impl de::Deserializer<Error> for IntDeserializer {
         #[inline]
-        fn end_of_stream_error(&self) -> Error {
+        fn end_of_stream_error(&mut self) -> Error {
             EndOfStream
         }
 
         #[inline]
-        fn syntax_error(&self, _token: de::Token, _expected: &[de::TokenKind]) -> Error {
+        fn syntax_error(&mut self, _token: de::Token, _expected: &[de::TokenKind]) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn missing_field_error(&self, _field: &'static str) -> Error {
+        fn missing_field_error(&mut self, _field: &'static str) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn unexpected_name_error(&self, _token: de::Token) -> Error {
+        fn unexpected_name_error(&mut self, _token: de::Token) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn conversion_error(&self, _token: de::Token) -> Error {
+        fn conversion_error(&mut self, _token: de::Token) -> Error {
             SyntaxError
         }
     }
@@ -365,27 +365,27 @@ mod deserializer {
 
     impl de::Deserializer<Error> for U8Deserializer {
         #[inline]
-        fn end_of_stream_error(&self) -> Error {
+        fn end_of_stream_error(&mut self) -> Error {
             EndOfStream
         }
 
         #[inline]
-        fn syntax_error(&self, _token: de::Token, _expected: &[de::TokenKind]) -> Error {
+        fn syntax_error(&mut self, _token: de::Token, _expected: &[de::TokenKind]) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn missing_field_error(&self, _field: &'static str) -> Error {
+        fn missing_field_error(&mut self, _field: &'static str) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn unexpected_name_error(&self, _token: de::Token) -> Error {
+        fn unexpected_name_error(&mut self, _token: de::Token) -> Error {
             SyntaxError
         }
 
         #[inline]
-        fn conversion_error(&self, _token: de::Token) -> Error {
+        fn conversion_error(&mut self, _token: de::Token) -> Error {
             SyntaxError
         }
     }
diff --git a/src/de.rs b/src/de.rs
index 37ec3556..88f1df60 100644
--- a/src/de.rs
+++ b/src/de.rs
@@ -176,15 +176,22 @@ macro_rules! to_result {
 }
 
 pub trait Deserializer<E>: Iterator<Result<Token, E>> {
-    fn end_of_stream_error(&self) -> E;
+    /// Called when a `Deserializable` expected more tokens, but the
+    /// `Deserializer` was empty.
+    fn end_of_stream_error(&mut self) -> E;
 
-    fn syntax_error(&self, token: Token, expected: &[TokenKind]) -> E;
+    /// Called when a `Deserializer` was unable to properly parse the stream.
+    fn syntax_error(&mut self, token: Token, expected: &[TokenKind]) -> E;
 
-    fn unexpected_name_error(&self, token: Token) -> E;
+    /// Called when a named structure or enum got a name that it didn't expect.
+    fn unexpected_name_error(&mut self, token: Token) -> E;
 
-    fn conversion_error(&self, token: Token) -> E;
+    /// Called when a value was unable to be coerced into another value.
+    fn conversion_error(&mut self, token: Token) -> E;
 
-    fn missing_field_error(&self, field: &'static str) -> E;
+    /// Called when a `Deserializable` structure did not deserialize a field
+    /// named `field`.
+    fn missing_field_error(&mut self, field: &'static str) -> E;
 
     #[inline]
     fn expect_token(&mut self) -> Result<Token, E> {
@@ -1132,23 +1139,23 @@ mod tests {
     }
 
     impl<Iter: Iterator<Token>> Deserializer<Error> for TokenDeserializer<Iter> {
-        fn end_of_stream_error(&self) -> Error {
+        fn end_of_stream_error(&mut self) -> Error {
             EndOfStream
         }
 
-        fn syntax_error(&self, _token: Token, _expected: &[TokenKind]) -> Error {
+        fn syntax_error(&mut self, _token: Token, _expected: &[TokenKind]) -> Error {
             SyntaxError
         }
 
-        fn unexpected_name_error(&self, _token: Token) -> Error {
+        fn unexpected_name_error(&mut self, _token: Token) -> Error {
             SyntaxError
         }
 
-        fn conversion_error(&self, _token: Token) -> Error {
+        fn conversion_error(&mut self, _token: Token) -> Error {
             SyntaxError
         }
 
-        fn missing_field_error(&self, _field: &'static str) -> Error {
+        fn missing_field_error(&mut self, _field: &'static str) -> Error {
             IncompleteValue
         }
     }
diff --git a/src/json/mod.rs b/src/json/mod.rs
index 1a47ab6c..4db5fd15 100644
--- a/src/json/mod.rs
+++ b/src/json/mod.rs
@@ -647,23 +647,23 @@ impl Iterator<Result<de::Token, ParserError>> for JsonDeserializer {
 }
 
 impl de::Deserializer<ParserError> for JsonDeserializer {
-    fn end_of_stream_error(&self) -> ParserError {
+    fn end_of_stream_error(&mut self) -> ParserError {
         SyntaxError(EOFWhileParsingValue, 0, 0)
     }
 
-    fn syntax_error(&self, _token: de::Token, _expected: &[de::TokenKind]) -> ParserError {
+    fn syntax_error(&mut self, _token: de::Token, _expected: &[de::TokenKind]) -> ParserError {
         SyntaxError(InvalidSyntax, 0, 0)
     }
 
-    fn unexpected_name_error(&self, _token: de::Token) -> ParserError {
+    fn unexpected_name_error(&mut self, _token: de::Token) -> ParserError {
         SyntaxError(InvalidSyntax, 0, 0)
     }
 
-    fn conversion_error(&self, _token: de::Token) -> ParserError {
+    fn conversion_error(&mut self, _token: de::Token) -> ParserError {
         SyntaxError(InvalidSyntax, 0, 0)
     }
 
-    fn missing_field_error(&self, field: &'static str) -> ParserError {
+    fn missing_field_error(&mut self, field: &'static str) -> ParserError {
         SyntaxError(MissingField(field), 0, 0)
     }
 
@@ -2023,23 +2023,23 @@ impl<T: Iterator<char>> Parser<T> {
 }
 
 impl<T: Iterator<char>> de::Deserializer<ParserError> for Parser<T> {
-    fn end_of_stream_error(&self) -> ParserError {
+    fn end_of_stream_error(&mut self) -> ParserError {
         SyntaxError(EOFWhileParsingValue, self.line, self.col)
     }
 
-    fn syntax_error(&self, _token: de::Token, _expected: &[de::TokenKind]) -> ParserError {
+    fn syntax_error(&mut self, _token: de::Token, _expected: &[de::TokenKind]) -> ParserError {
         SyntaxError(InvalidSyntax, self.line, self.col)
     }
 
-    fn unexpected_name_error(&self, _token: de::Token) -> ParserError {
+    fn unexpected_name_error(&mut self, _token: de::Token) -> ParserError {
         SyntaxError(InvalidSyntax, self.line, self.col)
     }
 
-    fn conversion_error(&self, _token: de::Token) -> ParserError {
+    fn conversion_error(&mut self, _token: de::Token) -> ParserError {
         SyntaxError(InvalidSyntax, self.line, self.col)
     }
 
-    fn missing_field_error(&self, field: &'static str) -> ParserError {
+    fn missing_field_error(&mut self, field: &'static str) -> ParserError {
         SyntaxError(MissingField(field), self.line, self.col)
     }