diff --git a/changelog.d/7822.bugfix b/changelog.d/7822.bugfix
new file mode 100644
index 000000000..faf249a67
--- /dev/null
+++ b/changelog.d/7822.bugfix
@@ -0,0 +1 @@
+Fix a bug causing Synapse to misinterpret the value `off` for `encryption_enabled_by_default_for_room_type` in its configuration file(s) if that value isn't surrounded by quotes. This bug was introduced in v1.16.0.
diff --git a/synapse/config/room.py b/synapse/config/room.py
index 6aa4de067..52cf0b62f 100644
--- a/synapse/config/room.py
+++ b/synapse/config/room.py
@@ -50,7 +50,12 @@ class RoomConfig(Config):
                 RoomCreationPreset.PRIVATE_CHAT,
                 RoomCreationPreset.TRUSTED_PRIVATE_CHAT,
             ]
-        elif encryption_for_room_type == RoomDefaultEncryptionTypes.OFF:
+        elif (
+            encryption_for_room_type == RoomDefaultEncryptionTypes.OFF
+            or encryption_for_room_type is False
+        ):
+            # PyYAML translates "off" into False if it's unquoted, so we also need to
+            # check for encryption_for_room_type being False.
             self.encryption_enabled_by_default_for_room_presets = []
         else:
             raise ConfigError(