diff --git a/lib/types/crypto-types.js b/lib/types/crypto-types.js
--- a/lib/types/crypto-types.js
+++ b/lib/types/crypto-types.js
@@ -127,7 +127,7 @@
 export const encryptedDataValidator: TInterface<EncryptedData> =
   tShape<EncryptedData>({
     message: t.String,
-    messageType: t.Number,
+    messageType: olmEncryptedMessageTypesValidator,
     sessionVersion: t.maybe(t.Number),
   });