diff --git a/ruma-client-api/Cargo.toml b/ruma-client-api/Cargo.toml
index a8e98b69..e08c005c 100644
--- a/ruma-client-api/Cargo.toml
+++ b/ruma-client-api/Cargo.toml
@@ -34,6 +34,7 @@ maplit = "1.0.2"
 matches = "0.1.8"
 
 [features]
+compat = []
 unstable-exhaustive-types = []
 unstable-pre-spec = []
 unstable-synapse-quirks = []
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 9fd7dcfa..769f67ec 100644
--- a/ruma-client-api/src/r0/profile/set_avatar_url.rs
+++ b/ruma-client-api/src/r0/profile/set_avatar_url.rs
@@ -22,6 +22,10 @@ ruma_api! {
         ///
         /// `None` is used to unset the avatar.
         #[serde(skip_serializing_if = "Option::is_none")]
+        #[cfg_attr(
+            feature = "compat",
+            serde(default, deserialize_with = "ruma_serde::empty_string_as_none")
+        )]
         pub avatar_url: Option<&'a str>,
     }
 
@@ -44,3 +48,37 @@ impl Response {
         Self
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use matches::assert_matches;
+    use ruma_api::IncomingRequest as _;
+
+    use super::IncomingRequest;
+
+    #[test]
+    fn deserialize_unset_request() -> Result<(), Box<dyn std::error::Error>> {
+        assert_matches!(
+            IncomingRequest::try_from_http_request(
+                http::Request::builder()
+                    .method("PUT")
+                    .uri("https://bar.org/_matrix/client/r0/profile/@foo:bar.org/avatar_url")
+                    .body(Vec::<u8>::new())?,
+            )?,
+            IncomingRequest { user_id, avatar_url: None } if user_id == "@foo:bar.org"
+        );
+
+        #[cfg(feature = "compat")]
+        assert_matches!(
+            IncomingRequest::try_from_http_request(
+                http::Request::builder()
+                    .method("PUT")
+                    .uri("https://bar.org/_matrix/client/r0/profile/@foo:bar.org/avatar_url")
+                    .body(serde_json::to_vec(&serde_json::json!({ "avatar_url": "" }))?)?,
+            )?,
+            IncomingRequest { user_id, avatar_url: None } if user_id == "@foo:bar.org"
+        );
+
+        Ok(())
+    }
+}
diff --git a/ruma/Cargo.toml b/ruma/Cargo.toml
index 594d3dc3..7fd40d1f 100644
--- a/ruma/Cargo.toml
+++ b/ruma/Cargo.toml
@@ -57,7 +57,7 @@ markdown = ["ruma-events/markdown"]
 #
 # For example, some mandatory string fields are defaulted to an empty string if
 # missing with this feature.
-compat = ["ruma-common/compat", "ruma-events/compat"]
+compat = ["ruma-common/compat", "ruma-events/compat", "ruma-client-api/compat"]
 
 # unstable: by using any of these, you opt out of all semver guarantees Ruma
 #           otherwise provides!