diff --git a/changelog.d/5906.feature b/changelog.d/5906.feature
new file mode 100644
index 000000000..7c789510a
--- /dev/null
+++ b/changelog.d/5906.feature
@@ -0,0 +1 @@
+Increase max display name size to 256.
diff --git a/synapse/handlers/profile.py b/synapse/handlers/profile.py
index 2cc237e6a..8690f69d4 100644
--- a/synapse/handlers/profile.py
+++ b/synapse/handlers/profile.py
@@ -34,7 +34,7 @@ from ._base import BaseHandler
 
 logger = logging.getLogger(__name__)
 
-MAX_DISPLAYNAME_LEN = 100
+MAX_DISPLAYNAME_LEN = 256
 MAX_AVATAR_URL_LEN = 1000