diff --git a/src/entry.rs b/src/entry.rs
index 7490ef1..df57dd8 100644
--- a/src/entry.rs
+++ b/src/entry.rs
@@ -464,13 +464,13 @@ impl Entry {
     /// # Examples
     ///
     /// ```
-    /// use std::collections::HashMap;
+    /// use std::collections::BTreeMap;
     /// use atom_syndication::Entry;
     /// use atom_syndication::extension::{ExtensionMap, Extension};
     ///
     /// let extension = Extension::default();
     ///
-    /// let mut item_map = HashMap::<String, Vec<Extension>>::new();
+    /// let mut item_map = BTreeMap::<String, Vec<Extension>>::new();
     /// item_map.insert("ext:name".to_string(), vec![extension]);
     ///
     /// let mut extension_map = ExtensionMap::default();
diff --git a/src/extension/mod.rs b/src/extension/mod.rs
index 41b8e0b..f4e9449 100644
--- a/src/extension/mod.rs
+++ b/src/extension/mod.rs
@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::BTreeMap;
 use std::io::Write;
 use std::str;
 
@@ -11,7 +11,7 @@ use crate::toxml::ToXml;
 pub(crate) mod util;
 
 /// A map of extension namespace prefixes to local names to elements.
-pub type ExtensionMap = HashMap<String, HashMap<String, Vec<Extension>>>;
+pub type ExtensionMap = BTreeMap<String, BTreeMap<String, Vec<Extension>>>;
 
 /// A namespaced extension.
 #[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
@@ -32,10 +32,10 @@ pub struct Extension {
     pub value: Option<String>,
     /// The attributes for the extension element.
     #[cfg_attr(feature = "builders", builder(setter(each = "attr")))]
-    pub attrs: HashMap<String, String>,
+    pub attrs: BTreeMap<String, String>,
     /// The children of the extension element. A map of local names to child elements.
     #[cfg_attr(feature = "builders", builder(setter(each = "child")))]
-    pub children: HashMap<String, Vec<Extension>>,
+    pub children: BTreeMap<String, Vec<Extension>>,
 }
 
 impl Extension {
@@ -108,16 +108,16 @@ impl Extension {
     /// # Examples
     ///
     /// ```
-    /// use std::collections::HashMap;
+    /// use std::collections::BTreeMap;
     /// use atom_syndication::extension::Extension;
     ///
     /// let mut extension = Extension::default();
-    /// let mut attrs = HashMap::<String, String>::new();
+    /// let mut attrs = BTreeMap::<String, String>::new();
     /// attrs.insert("email".to_string(), "johndoe@example.com".to_string());
     /// extension.set_attrs(attrs.clone());
     /// assert_eq!(*extension.attrs(), attrs);
     /// ```
-    pub fn attrs(&self) -> &HashMap<String, String> {
+    pub fn attrs(&self) -> &BTreeMap<String, String> {
         &self.attrs
     }
 
@@ -126,15 +126,15 @@ impl Extension {
     /// # Examples
     ///
     /// ```
-    /// use std::collections::HashMap;
+    /// use std::collections::BTreeMap;
     /// use atom_syndication::extension::Extension;
     ///
     /// let mut extension = Extension::default();
-    /// extension.set_attrs(HashMap::new());
+    /// extension.set_attrs(BTreeMap::new());
     /// ```
     pub fn set_attrs<V>(&mut self, attrs: V)
     where
-        V: Into<HashMap<String, String>>,
+        V: Into<BTreeMap<String, String>>,
     {
         self.attrs = attrs.into();
     }
@@ -146,16 +146,16 @@ impl Extension {
     /// # Examples
     ///
     /// ```
-    /// use std::collections::HashMap;
+    /// use std::collections::BTreeMap;
     /// use atom_syndication::extension::Extension;
     ///
     /// let mut extension = Extension::default();
-    /// let mut children = HashMap::<String, Vec<Extension>>::new();
+    /// let mut children = BTreeMap::<String, Vec<Extension>>::new();
     /// children.insert("ext:child".to_string(), Vec::new());
     /// extension.set_children(children);
     /// assert!(extension.children().contains_key("ext:child"));
     /// ```
-    pub fn children(&self) -> &HashMap<String, Vec<Extension>> {
+    pub fn children(&self) -> &BTreeMap<String, Vec<Extension>> {
         &self.children
     }
 
@@ -166,15 +166,15 @@ impl Extension {
     /// # Examples
     ///
     /// ```
-    /// use std::collections::HashMap;
+    /// use std::collections::BTreeMap;
     /// use atom_syndication::extension::Extension;
     ///
     /// let mut extension = Extension::default();
-    /// extension.set_children(HashMap::new());
+    /// extension.set_children(BTreeMap::new());
     /// ```
     pub fn set_children<V>(&mut self, children: V)
     where
-        V: Into<HashMap<String, Vec<Extension>>>,
+        V: Into<BTreeMap<String, Vec<Extension>>>,
     {
         self.children = children.into();
     }
diff --git a/src/extension/util.rs b/src/extension/util.rs
index 9d1fc34..48806ae 100644
--- a/src/extension/util.rs
+++ b/src/extension/util.rs
@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::BTreeMap;
 use std::io::BufRead;
 use std::str;
 
@@ -32,7 +32,7 @@ where
     let ext = parse_extension_element(reader, atts)?;
 
     if !extensions.contains_key(ns) {
-        extensions.insert(ns.to_string(), HashMap::new());
+        extensions.insert(ns.to_string(), BTreeMap::new());
     }
 
     let map = match extensions.get_mut(ns) {
diff --git a/src/feed.rs b/src/feed.rs
index 97cc45f..c0b9855 100644
--- a/src/feed.rs
+++ b/src/feed.rs
@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::BTreeMap;
 use std::io::{BufRead, Write};
 use std::str::{self, FromStr};
 
@@ -70,7 +70,7 @@ pub struct Feed {
     pub extensions: ExtensionMap,
     /// The namespaces present in the feed tag.
     #[cfg_attr(feature = "builders", builder(setter(each = "namespace")))]
-    pub namespaces: HashMap<String, String>,
+    pub namespaces: BTreeMap<String, String>,
 }
 
 impl Feed {
@@ -570,13 +570,13 @@ impl Feed {
     /// # Examples
     ///
     /// ```
-    /// use std::collections::HashMap;
+    /// use std::collections::BTreeMap;
     /// use atom_syndication::Feed;
     /// use atom_syndication::extension::{ExtensionMap, Extension};
     ///
     /// let extension = Extension::default();
     ///
-    /// let mut item_map = HashMap::<String, Vec<Extension>>::new();
+    /// let mut item_map = BTreeMap::<String, Vec<Extension>>::new();
     /// item_map.insert("ext:name".to_string(), vec![extension]);
     ///
     /// let mut extension_map = ExtensionMap::default();
@@ -617,17 +617,17 @@ impl Feed {
     /// # Examples
     ///
     /// ```
-    /// use std::collections::HashMap;
+    /// use std::collections::BTreeMap;
     /// use atom_syndication::Feed;
     ///
-    /// let mut namespaces = HashMap::new();
+    /// let mut namespaces = BTreeMap::new();
     /// namespaces.insert("ext".to_string(), "http://example.com".to_string());
     ///
     /// let mut feed = Feed::default();
     /// feed.set_namespaces(namespaces);
     /// assert_eq!(feed.namespaces().get("ext").map(|s| s.as_str()), Some("http://example.com"));
     /// ```
-    pub fn namespaces(&self) -> &HashMap<String, String> {
+    pub fn namespaces(&self) -> &BTreeMap<String, String> {
         &self.namespaces
     }
 
@@ -636,15 +636,15 @@ impl Feed {
     /// # Examples
     ///
     /// ```
-    /// use std::collections::HashMap;
+    /// use std::collections::BTreeMap;
     /// use atom_syndication::Feed;
     ///
     /// let mut feed = Feed::default();
-    /// feed.set_namespaces(HashMap::new());
+    /// feed.set_namespaces(BTreeMap::new());
     /// ```
     pub fn set_namespaces<V>(&mut self, namespaces: V)
     where
-        V: Into<HashMap<String, String>>,
+        V: Into<BTreeMap<String, String>>,
     {
         self.namespaces = namespaces.into()
     }
@@ -800,7 +800,7 @@ impl Default for Feed {
             subtitle: None,
             entries: Vec::new(),
             extensions: ExtensionMap::default(),
-            namespaces: HashMap::default(),
+            namespaces: BTreeMap::default(),
         }
     }
 }
diff --git a/tests/builders.rs b/tests/builders.rs
index b6fd675..d18176c 100644
--- a/tests/builders.rs
+++ b/tests/builders.rs
@@ -2,7 +2,7 @@
 
 use atom_syndication::extension::*;
 use atom_syndication::*;
-use std::collections::HashMap;
+use std::collections::BTreeMap;
 use std::str::FromStr;
 
 fn join_lines(text: &str) -> String {
@@ -79,7 +79,7 @@ fn test_builders() {
                         .build(),
                 )
                 .extension(("ext".to_string(), {
-                    let mut map = HashMap::new();
+                    let mut map = BTreeMap::new();
                     map.insert(
                         "title".to_string(),
                         vec![ExtensionBuilder::default()