diff --git a/hmm.json b/hmm.json
index 9edf20d30..5382504a6 100644
--- a/hmm.json
+++ b/hmm.json
@@ -109,7 +109,7 @@
       "name": "polymod",
       "type": "git",
       "dir": null,
-      "ref": "491fd0e",
+      "ref": "631a363",
       "url": "https://github.com/larsiusprime/polymod"
     },
     {