diff --git a/src/datetime.rs b/src/datetime.rs
index 83b5c0b..c67e2c4 100644
--- a/src/datetime.rs
+++ b/src/datetime.rs
@@ -40,8 +40,8 @@ pub struct DatetimeParseError {
 //
 // In general the TOML encoder/decoder will catch this and not literally emit
 // these strings but rather emit datetimes as they're intended.
-pub const SERDE_STRUCT_FIELD_NAME: &'static str = "$__toml_private_datetime";
-pub const SERDE_STRUCT_NAME: &'static str = "$__toml_private_Datetime";
+pub const FIELD: &'static str = "$__toml_private_datetime";
+pub const NAME: &'static str = "$__toml_private_Datetime";
 
 #[derive(PartialEq, Clone)]
 struct Date {
@@ -311,8 +311,8 @@ impl ser::Serialize for Datetime {
     {
         use serde::ser::SerializeStruct;
 
-        let mut s = serializer.serialize_struct(SERDE_STRUCT_NAME, 1)?;
-        s.serialize_field(SERDE_STRUCT_FIELD_NAME, &self.to_string())?;
+        let mut s = serializer.serialize_struct(NAME, 1)?;
+        s.serialize_field(FIELD, &self.to_string())?;
         s.end()
     }
 }
@@ -343,10 +343,8 @@ impl<'de> de::Deserialize<'de> for Datetime {
             }
         }
 
-        static FIELDS: [&'static str; 1] = [SERDE_STRUCT_FIELD_NAME];
-        deserializer.deserialize_struct(SERDE_STRUCT_NAME,
-                                        &FIELDS,
-                                        DatetimeVisitor)
+        static FIELDS: [&'static str; 1] = [FIELD];
+        deserializer.deserialize_struct(NAME, &FIELDS, DatetimeVisitor)
     }
 }
 
@@ -368,7 +366,7 @@ impl<'de> de::Deserialize<'de> for DatetimeKey {
             fn visit_str<E>(self, s: &str) -> Result<(), E>
                 where E: de::Error
             {
-                if s == SERDE_STRUCT_FIELD_NAME {
+                if s == FIELD {
                     Ok(())
                 } else {
                     Err(de::Error::custom("expected field with custom name"))
diff --git a/src/de.rs b/src/de.rs
index c80c065..cc1e2ca 100644
--- a/src/de.rs
+++ b/src/de.rs
@@ -14,7 +14,7 @@ use serde::de;
 use serde::de::IntoDeserializer;
 
 use tokens::{Tokenizer, Token, Error as TokenError, Span};
-use datetime::{SERDE_STRUCT_FIELD_NAME, SERDE_STRUCT_NAME};
+use datetime;
 use spanned;
 
 /// Deserializes a byte slice into a type.
@@ -536,7 +536,7 @@ impl<'de> de::Deserializer<'de> for ValueDeserializer<'de> {
                              visitor: V) -> Result<V::Value, Error>
         where V: de::Visitor<'de>,
     {
-        if name == SERDE_STRUCT_NAME && fields == &[SERDE_STRUCT_FIELD_NAME] {
+        if name == datetime::NAME && fields == &[datetime::FIELD] {
             if let E::Datetime(s) = self.value.e {
                 return visitor.visit_map(DatetimeDeserializer {
                     date: s,
@@ -545,9 +545,10 @@ impl<'de> de::Deserializer<'de> for ValueDeserializer<'de> {
             }
         }
 
-        if name == spanned::NAME && fields == spanned::FIELDS {
+        if name == spanned::NAME && fields == &[spanned::START, spanned::END, spanned::VALUE] {
             let start = self.value.start;
             let end = self.value.end;
+
             return visitor.visit_map(SpannedDeserializer {
                 start: Some(start),
                 value: Some(self.value),
@@ -607,8 +608,8 @@ impl<'de> de::IntoDeserializer<'de, Error> for Value<'de> {
 
 struct SpannedDeserializer<'a> {
     start: Option<usize>,
-    value: Option<Value<'a>>,
     end: Option<usize>,
+    value: Option<Value<'a>>,
 }
 
 impl<'de> de::MapAccess<'de> for SpannedDeserializer<'de> {
@@ -619,11 +620,11 @@ impl<'de> de::MapAccess<'de> for SpannedDeserializer<'de> {
         K: de::DeserializeSeed<'de>,
     {
         if self.start.is_some() {
-            seed.deserialize("start".into_deserializer()).map(Some)
-        } else if self.value.is_some() {
-            seed.deserialize("value".into_deserializer()).map(Some)
+            seed.deserialize(spanned::START.into_deserializer()).map(Some)
         } else if self.end.is_some() {
-            seed.deserialize("end".into_deserializer()).map(Some)
+            seed.deserialize(spanned::END.into_deserializer()).map(Some)
+        } else if self.value.is_some() {
+            seed.deserialize(spanned::VALUE.into_deserializer()).map(Some)
         } else {
             Ok(None)
         }
@@ -635,10 +636,10 @@ impl<'de> de::MapAccess<'de> for SpannedDeserializer<'de> {
     {
         if let Some(start) = self.start.take() {
             seed.deserialize(start.into_deserializer())
+        } else if  let Some(end) = self.end.take() {
+            seed.deserialize(end.into_deserializer())
         } else if let Some(value) = self.value.take() {
             seed.deserialize(value.into_deserializer())
-        } else if let Some(end) = self.end.take() {
-            seed.deserialize(end.into_deserializer())
         } else {
             panic!("next_value_seed called before next_key_seed")
         }
@@ -678,7 +679,7 @@ impl<'de> de::Deserializer<'de> for DatetimeFieldDeserializer {
     fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
         where V: de::Visitor<'de>,
     {
-        visitor.visit_borrowed_str(SERDE_STRUCT_FIELD_NAME)
+        visitor.visit_borrowed_str(datetime::FIELD)
     }
 
     forward_to_deserialize_any! {
@@ -811,21 +812,25 @@ impl<'a> Deserializer<'a> {
         let at = self.tokens.current();
         let value = match self.next()? {
             Some((Span { start, end }, Token::String { val, .. })) => {
-                Value { e: E::String(val), start, end }
+                Value { e: E::String(val), start: start, end: end }
             }
             Some((Span { start, end }, Token::Keylike("true"))) => {
-                Value { e: E::Boolean(true), start, end }
+                Value { e: E::Boolean(true), start: start, end: end }
             }
             Some((Span { start, end }, Token::Keylike("false"))) => {
-                Value { e: E::Boolean(false), start, end }
+                Value { e: E::Boolean(false), start: start, end: end }
             }
-            Some((_, Token::Keylike(key))) => self.number_or_date(key)?,
+            Some((span, Token::Keylike(key))) => self.number_or_date(span, key)?,
             Some((_, Token::Plus)) => self.number_leading_plus()?,
             Some((Span { start, end }, Token::LeftBrace)) => {
-                self.inline_table().map(|table| Value { e: E::InlineTable(table), start, end })?
+                self.inline_table().map(|table| Value {
+                    e: E::InlineTable(table),
+                    start: start,
+                    end: end
+                })?
             }
             Some((Span { start, end }, Token::LeftBracket)) => {
-                self.array().map(|array| Value { e: E::Array(array), start, end })?
+                self.array().map(|array| Value { e: E::Array(array), start: start, end: end })?
             }
             Some(token) => {
                 return Err(self.error(at, ErrorKind::Wanted {
@@ -838,42 +843,49 @@ impl<'a> Deserializer<'a> {
         Ok(value)
     }
 
-    fn number_or_date(&mut self, s: &'a str) -> Result<Value<'a>, Error> {
+    fn number_or_date(&mut self, span: Span, s: &'a str)
+        -> Result<Value<'a>, Error>
+    {
         if s.contains('T') || (s.len() > 1 && s[1..].contains('-')) &&
            !s.contains("e-") {
-            // FIXME needs span
-            self.datetime(s, false).map(|d| Value { e: E::Datetime(d), start: 0, end: 0 })
+            self.datetime(s, false).map(|d| Value {
+                e: E::Datetime(d),
+                start: span.start,
+                end: span.end
+            })
         } else if self.eat(Token::Colon)? {
-            // FIXME needs span
-            self.datetime(s, true).map(|d| Value { e: E::Datetime(d), start: 0, end: 0 })
+            self.datetime(s, true).map(|d| Value {
+                e: E::Datetime(d),
+                start: span.start,
+                end: span.end
+            })
         } else {
-            self.number(s)
+            self.number(span, s)
         }
     }
 
-    fn number(&mut self, s: &'a str) -> Result<Value<'a>, Error> {
+    fn number(&mut self, Span { start, end}: Span, s: &'a str) -> Result<Value<'a>, Error> {
         if s.contains('e') || s.contains('E') {
-            // FIXME needs span
-            self.float(s, None).map(|f| Value { e: E::Float(f), start: 0, end: 0 })
+            self.float(s, None).map(|f| Value { e: E::Float(f), start: start, end: end })
         } else if self.eat(Token::Period)? {
             let at = self.tokens.current();
             match self.next()? {
-                Some((_, Token::Keylike(after))) => {
-                    // FIXME needs span
-                    self.float(s, Some(after)).map(|f| Value { e: E::Float(f), start: 0, end: 0 })
+                Some((Span { start, end }, Token::Keylike(after))) => {
+                    self.float(s, Some(after)).map(|f| Value {
+                        e: E::Float(f), start: start, end: end
+                    })
                 }
                 _ => Err(self.error(at, ErrorKind::NumberInvalid)),
             }
         } else {
-            // FIXME needs span
-            self.integer(s).map(|f| Value { e: E::Integer(f), start: 0, end: 0 })
+            self.integer(s).map(|f| Value { e: E::Integer(f), start: start, end: end })
         }
     }
 
     fn number_leading_plus(&mut self) -> Result<Value<'a>, Error> {
         let start = self.tokens.current();
         match self.next()? {
-            Some((_, Token::Keylike(s))) => self.number(s),
+            Some((span, Token::Keylike(s))) => self.number(span, s),
             _ => Err(self.error(start, ErrorKind::NumberInvalid)),
         }
     }
diff --git a/src/lib.rs b/src/lib.rs
index cc7bc41..f42512f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -173,3 +173,4 @@ mod tokens;
 pub mod macros;
 
 pub mod spanned;
+pub use spanned::Spanned;
diff --git a/src/ser.rs b/src/ser.rs
index 58c0b42..b8cec35 100644
--- a/src/ser.rs
+++ b/src/ser.rs
@@ -33,7 +33,7 @@ use std::marker;
 use std::rc::Rc;
 
 use serde::ser;
-use datetime::{SERDE_STRUCT_FIELD_NAME, SERDE_STRUCT_NAME};
+use datetime;
 
 /// Serialize the given data structure as a TOML byte vector.
 ///
@@ -924,7 +924,7 @@ impl<'a, 'b> ser::Serializer for &'b mut Serializer<'a> {
 
     fn serialize_struct(self, name: &'static str, _len: usize)
                         -> Result<Self::SerializeStruct, Self::Error> {
-        if name == SERDE_STRUCT_NAME {
+        if name == datetime::NAME {
             self.array_type("datetime")?;
             Ok(SerializeTable::Datetime(self))
         } else {
@@ -1071,7 +1071,7 @@ impl<'a, 'b> ser::SerializeStruct for SerializeTable<'a, 'b> {
     {
         match *self {
             SerializeTable::Datetime(ref mut ser) => {
-                if key == SERDE_STRUCT_FIELD_NAME {
+                if key == datetime::FIELD {
                     value.serialize(DateStrEmitter(&mut *ser))?;
                 } else {
                     return Err(Error::DateInvalid)
diff --git a/src/spanned.rs b/src/spanned.rs
index 04ec9b8..1673d66 100644
--- a/src/spanned.rs
+++ b/src/spanned.rs
@@ -6,43 +6,147 @@
 //! use toml::spanned::Spanned;
 //!
 //! #[derive(Deserialize)]
-//! struct Udoprog {
+//! struct Value {
 //!     s: Spanned<String>,
 //! }
 //!
 //! fn main() {
-//!     let t = "s = \"udoprog\"\n";
+//!     let t = "s = \"value\"\n";
 //!
-//!     let u: Udoprog = toml::from_str(t).unwrap();
+//!     let u: Value = toml::from_str(t).unwrap();
 //!
 //!     assert_eq!(u.s.start, 4);
-//!     assert_eq!(u.s.end, 13);
+//!     assert_eq!(u.s.end, 11);
 //! }
 //! ```
 
-use serde::{Serialize, Serializer};
+use serde::{de, ser};
+use std::fmt;
 
-// FIXME: use a more unique name like "toml::Spanned".
 #[doc(hidden)]
-pub const NAME: &str = "Spanned";
+pub const NAME: &'static str = "$__toml_private_Spanned";
 #[doc(hidden)]
-pub const FIELDS: &[&str] = &["value", "start", "end"];
+pub const START: &'static str = "$__toml_private_start";
+#[doc(hidden)]
+pub const END: &'static str = "$__toml_private_end";
+#[doc(hidden)]
+pub const VALUE: &'static str = "$__toml_private_value";
 
-///
-#[derive(Deserialize, Debug)]
-pub struct Spanned<T> {
-    ///
-    pub value: T,
-    ///
-    pub start: usize,
-    ///
-    pub end: usize,
+macro_rules! key_deserialize {
+    ($ident:ident, $field:expr, $name:expr) => {
+        struct $ident;
+
+        impl<'de> de::Deserialize<'de> for $ident {
+            fn deserialize<D>(deserializer: D) -> Result<$ident, D::Error>
+                where D: de::Deserializer<'de>
+            {
+                struct FieldVisitor;
+
+                impl<'de> de::Visitor<'de> for FieldVisitor {
+                    type Value = ();
+
+                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                        formatter.write_str("a valid spanned field")
+                    }
+
+                    fn visit_str<E>(self, s: &str) -> Result<(), E>
+                        where E: de::Error
+                    {
+                        if s == $field {
+                            Ok(())
+                        } else {
+                            Err(de::Error::custom(
+                                concat!("expected spanned field `", $name, "`")))
+                        }
+                    }
+                }
+
+                deserializer.deserialize_identifier(FieldVisitor)?;
+                Ok($ident)
+            }
+        }
+    }
 }
 
-impl<T: Serialize> Serialize for Spanned<T> {
+
+/// A spanned value, indicating the range at which it is defined in the source.
+#[derive(Debug)]
+pub struct Spanned<T> {
+    /// The start range.
+    pub start: usize,
+    /// The end range (exclusive).
+    pub end: usize,
+    /// The spanned value.
+    pub value: T,
+}
+
+impl<'de, T> de::Deserialize<'de> for Spanned<T>
+    where T: de::Deserialize<'de>
+{
+    fn deserialize<D>(deserializer: D) -> Result<Spanned<T>, D::Error>
+        where D: de::Deserializer<'de>
+    {
+        struct SpannedVisitor<T>(::std::marker::PhantomData<T>);
+
+        impl<'de, T> de::Visitor<'de> for SpannedVisitor<T>
+            where T: de::Deserialize<'de>
+        {
+            type Value = Spanned<T>;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("a TOML spanned")
+            }
+
+            fn visit_map<V>(self, mut visitor: V) -> Result<Spanned<T>, V::Error>
+                where V: de::MapAccess<'de>
+            {
+                let start = visitor.next_key::<StartKey>()?;
+
+                if start.is_none() {
+                    return Err(de::Error::custom("spanned start key not found"))
+                }
+
+                let start: usize = visitor.next_value()?;
+
+                let end = visitor.next_key::<EndKey>()?;
+
+                if end.is_none() {
+                    return Err(de::Error::custom("spanned end key not found"))
+                }
+
+                let end: usize = visitor.next_value()?;
+
+                let value = visitor.next_key::<ValueKey>()?;
+
+                if value.is_none() {
+                    return Err(de::Error::custom("spanned value key not found"))
+                }
+
+                let value: T = visitor.next_value()?;
+
+                Ok(Spanned {
+                    start: start,
+                    end: end,
+                    value: value
+                })
+            }
+        }
+
+        key_deserialize!(StartKey, START, "start");
+        key_deserialize!(EndKey, END, "end");
+        key_deserialize!(ValueKey, VALUE, "value");
+
+        let visitor = SpannedVisitor(::std::marker::PhantomData);
+
+        static FIELDS: [&'static str; 3] = [START, END, VALUE];
+        deserializer.deserialize_struct(NAME, &FIELDS, visitor)
+    }
+}
+
+impl<T: ser::Serialize> ser::Serialize for Spanned<T> {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
-        S: Serializer,
+        S: ser::Serializer,
     {
         self.value.serialize(serializer)
     }
diff --git a/src/value.rs b/src/value.rs
index 54fa45c..21a8205 100644
--- a/src/value.rs
+++ b/src/value.rs
@@ -12,7 +12,7 @@ use serde::de;
 use serde::de::IntoDeserializer;
 
 pub use datetime::{Datetime, DatetimeParseError};
-use datetime::{DatetimeFromString, SERDE_STRUCT_FIELD_NAME};
+use datetime::{self, DatetimeFromString};
 
 /// Representation of a TOML value.
 #[derive(PartialEq, Clone, Debug)]
@@ -925,7 +925,7 @@ impl<'a, 'de> de::Visitor<'de> for DatetimeOrTable<'a> {
     fn visit_str<E>(self, s: &str) -> Result<bool, E>
         where E: de::Error,
     {
-        if s == SERDE_STRUCT_FIELD_NAME {
+        if s == datetime::FIELD {
             Ok(true)
         } else {
             self.key.push_str(s);
@@ -936,7 +936,7 @@ impl<'a, 'de> de::Visitor<'de> for DatetimeOrTable<'a> {
     fn visit_string<E>(self, s: String) -> Result<bool, E>
         where E: de::Error,
     {
-        if s == SERDE_STRUCT_FIELD_NAME {
+        if s == datetime::FIELD {
             Ok(true)
         } else {
             *self.key = s;
diff --git a/test-suite/tests/spanned.rs b/test-suite/tests/spanned.rs
new file mode 100644
index 0000000..fec9ea8
--- /dev/null
+++ b/test-suite/tests/spanned.rs
@@ -0,0 +1,30 @@
+extern crate serde;
+extern crate toml;
+#[macro_use]
+extern crate serde_derive;
+
+use toml::Spanned;
+use std::collections::HashMap;
+
+#[test]
+fn test_spanned_field() {
+    #[derive(Deserialize)]
+    struct Foo<T> {
+        foo: Spanned<T>,
+    }
+
+    fn good<'de, T>(s: &'de str, expected: &str) where T: serde::Deserialize<'de> {
+        let foo: Foo<T> = toml::from_str(s).unwrap();
+
+        assert_eq!(6, foo.foo.start);
+        assert_eq!(s.len(), foo.foo.end);
+        assert_eq!(expected, &s[foo.foo.start..foo.foo.end]);
+    }
+
+    good::<String>("foo = \"foo\"", "\"foo\"");
+    good::<u32>("foo = 42", "42");
+    good::<HashMap<String, u32>>(
+        "foo = {\"foo\" = 42, \"bar\" = 42}",
+        "{\"foo\" = 42, \"bar\" = 42}"
+    );
+}