diff --git a/src/crypto/algorithms/megolm.js b/src/crypto/algorithms/megolm.js
index 7534b3ed1..005d157c5 100644
--- a/src/crypto/algorithms/megolm.js
+++ b/src/crypto/algorithms/megolm.js
@@ -543,7 +543,7 @@ MegolmEncryption.prototype._getDevicesInRoom = function(room) {
 
     // The global value is treated as a default for when rooms don't specify a value.
     let isBlacklisting = this._crypto.getGlobalBlacklistUnverifiedDevices();
-    if (room.getBlacklistUnverifiedDevices() !== null) {
+    if (typeof room.getBlacklistUnverifiedDevices() === 'boolean') {
         isBlacklisting = room.getBlacklistUnverifiedDevices();
     }