diff --git a/changelog.d/6691.misc b/changelog.d/6691.misc
new file mode 100644
index 000000000000..104e9ce64823
--- /dev/null
+++ b/changelog.d/6691.misc
@@ -0,0 +1 @@
+Remove redundant RegistrationError class.
diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index 5853a54c9517..9e9844b47c30 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -158,12 +158,6 @@ def __init__(self, msg):
         )
 
 
-class RegistrationError(SynapseError):
-    """An error raised when a registration event fails."""
-
-    pass
-
-
 class FederationDeniedError(SynapseError):
     """An error raised when the server tries to federate with a server which
     is not on its federation whitelist.
diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index 885da829859d..7ffc194f0c67 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -20,13 +20,7 @@
 
 from synapse import types
 from synapse.api.constants import MAX_USERID_LENGTH, LoginType
-from synapse.api.errors import (
-    AuthError,
-    Codes,
-    ConsentNotGivenError,
-    RegistrationError,
-    SynapseError,
-)
+from synapse.api.errors import AuthError, Codes, ConsentNotGivenError, SynapseError
 from synapse.config.server import is_threepid_reserved
 from synapse.http.servlet import assert_params_in_dict
 from synapse.replication.http.login import RegisterDeviceReplicationServlet
@@ -165,7 +159,7 @@ def register_user(
         Returns:
             Deferred[str]: user_id
         Raises:
-            RegistrationError if there was a problem registering.
+            SynapseError if there was a problem registering.
         """
         yield self.check_registration_ratelimit(address)
 
@@ -182,7 +176,7 @@ def register_user(
             if not was_guest:
                 try:
                     int(localpart)
-                    raise RegistrationError(
+                    raise SynapseError(
                         400, "Numeric user IDs are reserved for guest users."
                     )
                 except ValueError:
diff --git a/tests/handlers/test_register.py b/tests/handlers/test_register.py
index 1e9ba3a201e8..e2915eb7b174 100644
--- a/tests/handlers/test_register.py
+++ b/tests/handlers/test_register.py
@@ -269,8 +269,6 @@ def get_or_create_user(self, requester, localpart, displayname, password_hash=No
               one will be randomly generated.
         Returns:
             A tuple of (user_id, access_token).
-        Raises:
-            RegistrationError if there was a problem registering.
         """
         if localpart is None:
             raise SynapseError(400, "Request must include user id")