diff --git a/src/lib.rs b/src/lib.rs
index 50698bc..f4271de 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -109,6 +109,10 @@ pub fn parse_response_vec<'a, I: Iterator<Item = &'a str>, T: de::DeserializeOwn
 /// Parse the `playlist` command, a list of key-value pairs, as a vector of filenames.
 /// The playlist index of each item is *not* included because, if needed,
 /// it can easily be added with `.enumerate()`.
+///
+/// Note: The MPD protocol documentation suggests using `playlistinfo` instead,
+/// which returns a superset of this commands output,
+/// but this isn’t deprecated, so if you only need the filenames, it should be all you need.
 pub fn parse_playlist<'a, I: Iterator<Item = &'a str>>(input: I) -> MpdResult<Vec<&'a str>> {
   input
     // `iter.scan((), |(), item| predicate(item))` is equivalent to map_while(predicate),
@@ -433,7 +437,7 @@ OK";
         File {
           name: "Scans".into(),
           last_modified: DateTime::parse_from_rfc3339("2015-01-30T14:53:03Z").unwrap(),
-          size: 0
+          size: -1
         },
         File {
           name: "15 風ハ旅スル（スマートフォンゲーム「風パズル 黒猫と白猫の夢見た世界」テーマ曲）.flac".into(),
diff --git a/src/structs.rs b/src/structs.rs
index f5fb8e3..c554999 100644
--- a/src/structs.rs
+++ b/src/structs.rs
@@ -117,19 +117,33 @@ pub struct Status {
   pub error: Option<String>,
 }
 
+/// An object in the file system, as returned by the `listfiles` command.
+/// For directories, the `size` will be `-1`, and [`is_directory`] is provided to check that.
+///
+/// [`is_directory`]: #method.is_directory
+///
+/// Properly parsing `listfiles` into a Vector of some enum with variants for file and directory
+/// would make the deserialization code a lot more complicated, so I’m not interested in doing that
+/// at this point in time.
 #[derive(Deserialize, Clone, Debug, PartialEq)]
 pub struct File {
   #[serde(alias = "directory", rename = "file")]
   pub name: String,
   #[serde(rename = "last-modified")]
   pub last_modified: DateTime<FixedOffset>,
-  #[serde(default)]
-  pub size: usize,
+  #[serde(default = "minus_one")]
+  pub size: i64,
+}
+
+fn minus_one() -> i64 {
+  -1
 }
 
 impl File {
+  /// Returns true if this file is a directory.
+  /// Internally, this just checks if `size == -1`.
   pub fn is_directory(&self) -> bool {
-    self.size == 0
+    self.size == -1
   }
 }