diff --git a/changelog.d/4592.feature b/changelog.d/4592.feature
new file mode 100644
index 000000000..112005ded
--- /dev/null
+++ b/changelog.d/4592.feature
@@ -0,0 +1,2 @@
+Allow the "unavailable" presence status for /sync.
+This change makes Synapse compliant with r0.4.0 of the Client-Server specification.
diff --git a/synapse/rest/client/v2_alpha/sync.py b/synapse/rest/client/v2_alpha/sync.py
index 025114672..39d157a44 100644
--- a/synapse/rest/client/v2_alpha/sync.py
+++ b/synapse/rest/client/v2_alpha/sync.py
@@ -75,7 +75,7 @@ class SyncRestServlet(RestServlet):
     """
 
     PATTERNS = client_v2_patterns("/sync$")
-    ALLOWED_PRESENCE = set(["online", "offline"])
+    ALLOWED_PRESENCE = set(["online", "offline", "unavailable"])
 
     def __init__(self, hs):
         super(SyncRestServlet, self).__init__()
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index 29e62bfcd..27e7cbf3c 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -38,6 +38,7 @@ class VersionsRestServlet(RestServlet):
                 "r0.1.0",
                 "r0.2.0",
                 "r0.3.0",
+                "r0.4.0",
             ],
             # as per MSC1497:
             "unstable_features": {