diff --git a/ciborium/src/ser/mod.rs b/ciborium/src/ser/mod.rs
index 89766e1..27ef0ee 100644
--- a/ciborium/src/ser/mod.rs
+++ b/ciborium/src/ser/mod.rs
@@ -400,11 +400,25 @@ macro_rules! end_map {
                     self.serializer.encoder.write_all(&key)?;
                     self.serializer.encoder.write_all(&value)?;
                 }
-            }
+            } else if matches!(self.serializer.canonicalization, CanonicalizationScheme::Rfc7049) {
+                // keys get sorted in length-first byte order
+                let keys = self.cache_keys;
+                let values = self.cache_values;
 
-            #[cfg(feature = "std")]
-            if matches!(self.serializer.canonicalization, CanonicalizationScheme::Rfc7049) {
-                unimplemented!("rfc7049 canonicalization not yet implemented");
+                debug_assert_eq!(
+                    keys.len(), values.len(),
+                    "ciborium error: canonicalization failed, different number of keys and values?");
+
+                let pairs: std::collections::BTreeMap<_, _> =
+                    keys.iter()
+                        .map(|key| (key.len(), key))
+                        .zip(values.iter())
+                        .collect();
+
+                for ((_, key), value) in pairs.iter() {
+                    self.serializer.encoder.write_all(&key)?;
+                    self.serializer.encoder.write_all(&value)?;
+                }
             }
 
             if self.indefinite {
diff --git a/ciborium/tests/canonical.rs b/ciborium/tests/canonical.rs
index ed3786b..50dbdfb 100644
--- a/ciborium/tests/canonical.rs
+++ b/ciborium/tests/canonical.rs
@@ -44,7 +44,7 @@ fn rfc8949_example() {
 }
 
 #[test]
-fn map() {
+fn map_old() {
     let mut map = BTreeMap::new();
     map.insert(cval!(false), val!(2));
     map.insert(cval!([-1]), val!(5));
@@ -64,6 +64,27 @@ fn map() {
     );
 }
 
+/// Use length-first ordering for keys.
+#[test]
+fn map_rfc7049() {
+    let mut map = BTreeMap::new();
+    map.insert(cval!(false), val!(2));
+    map.insert(cval!([-1]), val!(5));
+    map.insert(cval!(-1), val!(1));
+    map.insert(cval!(10), val!(0));
+    map.insert(cval!(100), val!(3));
+    map.insert(cval!([100]), val!(7));
+    map.insert(cval!("z"), val!(4));
+    map.insert(cval!("aa"), val!(6));
+
+    let bytes1 = ciborium::ser::to_vec_canonical(&map, CanonicalizationScheme::Rfc7049).unwrap();
+
+    assert_eq!(
+        hex::encode(&bytes1),
+        "a80a002001f402186403617a048120056261610681186407"
+    );
+}
+
 /// Match [RFC 8949] deterministic ordering example.
 ///
 /// The RFC specifies lexicographic byte ordering of serialized keys.
@@ -71,7 +92,7 @@ fn map() {
 /// [RFC 8949]: https://www.rfc-editor.org/rfc/rfc8949.html#name-core-deterministic-encoding
 #[test]
 #[cfg(feature = "std")]
-fn map_canonical() {
+fn map_rfc8949() {
     let mut map = BTreeMap::new();
     map.insert(cval!(false), val!(2));
     map.insert(cval!([-1]), val!(5));