diff --git a/compiler/bootstrap/compilation/x64/64/x64_config_encScript.sml b/compiler/bootstrap/compilation/x64/64/x64_config_encScript.sml
index 246345e9da..a630675701 100644
--- a/compiler/bootstrap/compilation/x64/64/x64_config_encScript.sml
+++ b/compiler/bootstrap/compilation/x64/64/x64_config_encScript.sml
@@ -11,7 +11,8 @@ val confs = LIST_CONJ
    to_dataBootstrapTheory.bvi_conf_def]
 
 val encode_backend_config_cake_config_lemma =
-  “encode_backend_config (config_to_inc_config cake_config)”
+  “encode_backend_config $ config_to_inc_config $ cake_config with <|
+     word_to_word_conf := (cake_config.word_to_word_conf with reg_alg := 4) |>”
   |> (SIMP_CONV (srw_ss()) [cake_config_def,confs,encode_backend_config_def] THENC EVAL);
 
 Definition config_enc_str_def: