diff --git a/bip-0341.mediawiki b/bip-0341.mediawiki
index 9bc8723b76..8d2af3ccc6 100644
--- a/bip-0341.mediawiki
+++ b/bip-0341.mediawiki
@@ -249,7 +249,10 @@ TapTweak = tagged_hash("TapTweak", p + ABCDE)
 
 <source lang="python">
 def taproot_sign_key(script_tree, internal_seckey, hash_type, bip340_aux_rand):
-    _, h = taproot_tree_helper(script_tree)
+    if script_tree is None:
+        h = bytes()
+    else:
+        _, h = taproot_tree_helper(script_tree)
     output_seckey = taproot_tweak_seckey(internal_seckey, h)
     sig = schnorr_sign(sighash(hash_type), output_seckey, bip340_aux_rand)
     if hash_type != 0: