diff --git a/python/tests/beagle_numba.py b/python/tests/beagle_numba.py
index a41b7c061a..571eab382e 100644
--- a/python/tests/beagle_numba.py
+++ b/python/tests/beagle_numba.py
@@ -507,8 +507,8 @@ def run_tsimpute(
     # WARN: Be careful with argument `acgt_alleles`!!!
     ls_hmm = _tskit.LsHmm(
         ref_ts_typed._ll_tree_sequence,
-        rho,
-        mu,
+        recombination_rate=rho,
+        mutation_rate=mu,
         acgt_alleles=True,
         precision=precision,
     )