diff --git a/ruma-client-api/CHANGELOG.md b/ruma-client-api/CHANGELOG.md
index 2350d7ed..1339021e 100644
--- a/ruma-client-api/CHANGELOG.md
+++ b/ruma-client-api/CHANGELOG.md
@@ -5,6 +5,7 @@ Bug fixes:
 * Fix deserialization of `r0::room::get_room_event::Response`
 * More missing fields in `r0::sync::sync_events::Response` can be deserialized
 * Fix `get_tags::Response` serialization
+* Fix unsetting avatar URL when `compat` feature is enabled
 
 Breaking changes:
 
diff --git a/ruma-client-api/src/r0/profile/set_avatar_url.rs b/ruma-client-api/src/r0/profile/set_avatar_url.rs
index e877bead..026f9021 100644
--- a/ruma-client-api/src/r0/profile/set_avatar_url.rs
+++ b/ruma-client-api/src/r0/profile/set_avatar_url.rs
@@ -24,10 +24,17 @@ ruma_api! {
         ///
         /// If you activate the `compat` feature, this field being an empty string in JSON will give
         /// you `None` here.
-        #[serde(skip_serializing_if = "Option::is_none")]
         #[cfg_attr(
             feature = "compat",
-            serde(default, deserialize_with = "ruma_serde::empty_string_as_none")
+            serde(
+                default,
+                deserialize_with = "ruma_serde::empty_string_as_none",
+                serialize_with = "ruma_serde::none_as_empty_string"
+            )
+        )]
+        #[cfg_attr(
+            not(feature = "compat"),
+            serde(skip_serializing_if = "Option::is_none")
         )]
         pub avatar_url: Option<&'a MxcUri>,
     }
diff --git a/ruma-serde/CHANGELOG.md b/ruma-serde/CHANGELOG.md
index 42b3b9cb..c2bcc700 100644
--- a/ruma-serde/CHANGELOG.md
+++ b/ruma-serde/CHANGELOG.md
@@ -4,6 +4,10 @@ Breaking changes:
 
 * Remove the `empty` module from the public API
 
+Improvements:
+
+* Add serialization decorator `none_as_empty_string` to serialize `None`s as empty strings
+
 # 0.3.1
 
 Bug fixes:
diff --git a/ruma-serde/src/lib.rs b/ruma-serde/src/lib.rs
index 6d137a57..3f572086 100644
--- a/ruma-serde/src/lib.rs
+++ b/ruma-serde/src/lib.rs
@@ -28,6 +28,7 @@ pub use empty::vec_as_map_of_empty;
 pub use raw::Raw;
 pub use strings::{
     btreemap_int_or_string_to_int_values, empty_string_as_none, int_or_string_to_int,
+    none_as_empty_string,
 };
 
 /// Check whether a value is equal to its default value.
diff --git a/ruma-serde/src/strings.rs b/ruma-serde/src/strings.rs
index 68ccb814..b1cef542 100644
--- a/ruma-serde/src/strings.rs
+++ b/ruma-serde/src/strings.rs
@@ -3,7 +3,8 @@ use std::{collections::BTreeMap, convert::TryInto, fmt, marker::PhantomData};
 use js_int::Int;
 use serde::{
     de::{self, Deserializer, IntoDeserializer as _, MapAccess, Visitor},
-    Deserialize,
+    ser::Serializer,
+    Deserialize, Serialize,
 };
 
 /// Serde deserialization decorator to map empty Strings to None,
@@ -30,6 +31,24 @@ where
     }
 }
 
+/// Serde serializiation decorator to map None to an empty String,
+/// and forward Somes to the Serialize implemention for T.
+///
+/// To be used like this:
+/// `#[serde(serialize_with = "empty_string_as_none")]`
+pub fn none_as_empty_string<T: Serialize, S>(
+    value: &Option<T>,
+    serializer: S,
+) -> Result<S::Ok, S::Error>
+where
+    S: Serializer,
+{
+    match value {
+        Some(x) => x.serialize(serializer),
+        None => serializer.serialize_str(""),
+    }
+}
+
 /// Take either an integer number or a string and deserialize to an integer number.
 ///
 /// To be used like this:
diff --git a/ruma-serde/tests/empty_strings.rs b/ruma-serde/tests/empty_strings.rs
new file mode 100644
index 00000000..b93665d9
--- /dev/null
+++ b/ruma-serde/tests/empty_strings.rs
@@ -0,0 +1,33 @@
+use serde::{Deserialize, Serialize};
+use serde_json::{from_value as from_json_value, json, to_value as to_json_value};
+
+#[derive(Serialize, Deserialize, PartialEq, Debug)]
+struct StringStruct {
+    #[serde(
+        deserialize_with = "ruma_serde::empty_string_as_none",
+        serialize_with = "ruma_serde::none_as_empty_string"
+    )]
+    x: Option<String>,
+}
+
+#[derive(Serialize, Deserialize, PartialEq, Debug)]
+struct NoneStruct {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    x: Option<String>,
+}
+
+#[test]
+fn empty_se() {
+    let string = StringStruct { x: None };
+    let none = NoneStruct { x: None };
+    assert_eq!(to_json_value(string).unwrap(), json!({"x": ""}));
+    assert_eq!(to_json_value(none).unwrap(), json!({}));
+}
+
+#[test]
+fn empty_de() {
+    let string = StringStruct { x: None };
+    let none = NoneStruct { x: None };
+    assert_eq!(from_json_value::<StringStruct>(json!({"x": ""})).unwrap(), string);
+    assert_eq!(from_json_value::<NoneStruct>(json!({})).unwrap(), none);
+}