diff --git a/python/_tskitmodule.c b/python/_tskitmodule.c
index 0d89a677dc..fde6da8b19 100644
--- a/python/_tskitmodule.c
+++ b/python/_tskitmodule.c
@@ -13259,12 +13259,12 @@ LsHmm_forward_matrix(LsHmm *self, PyObject *args)
         = tsk_ls_hmm_forward(self->ls_hmm, PyArray_DATA(haplotype_array),
             compressed_matrix->compressed_matrix, TSK_NO_INIT);
     Py_END_ALLOW_THREADS
-        // clang-format on
-        if (err != 0)
+    if (err != 0)
     {
         handle_library_error(err);
         goto out;
     }
+    // clang-format on
     ret = Py_BuildValue("");
 out:
     Py_XDECREF(haplotype_array);