diff --git a/src/client.js b/src/client.js
index 3503530b7..00cf2824d 100644
--- a/src/client.js
+++ b/src/client.js
@@ -1505,8 +1505,11 @@ MatrixClient.prototype.createKeyBackupVersion = async function(info) {
     // favour of just signing with the cross-singing master key.
     await this._crypto._signObject(data.auth_data);
 
-    if (this._crypto._crossSigningInfo.getId()) {
+    if (this._cryptoCallbacks.getSecretStorageKey && this._crypto._crossSigningInfo.getId()) {
         // now also sign the auth data with the cross-signing master key
+        // we check for the callback explicitly here because we still want to be able
+        // to create an un-cross-signed key backup if there is a cross-signing key but
+        // no callback supplied.
         await this._crypto._crossSigningInfo.signObject(data.auth_data, "master");
     }