diff --git a/gmrflib/graph.c b/gmrflib/graph.c
index 3d04b6e6e..e3d3c3c46 100644
--- a/gmrflib/graph.c
+++ b/gmrflib/graph.c
@@ -2082,7 +2082,6 @@ int GMRFLib_graph_union(GMRFLib_graph_tp **union_graph, GMRFLib_graph_tp **graph
 		GMRFLib_ged_insert_graph(ged, graph_array[i], 0);
 	}
 	GMRFLib_ged_build(union_graph, ged);
-	GMRFLib_graph_prepare(*union_graph);
 	GMRFLib_ged_free(ged);
 
 	return GMRFLib_SUCCESS;
diff --git a/gmrflib/pre-opt.c b/gmrflib/pre-opt.c
index 9f8d73c64..aefd9a764 100644
--- a/gmrflib/pre-opt.c
+++ b/gmrflib/pre-opt.c
@@ -370,9 +370,11 @@ int GMRFLib_preopt_init(GMRFLib_preopt_tp **preopt, int npred, int nf, int **c,
 		GMRFLib_idxval_free(ivs[k]);
 	}
 
-	GMRFLib_idxval_to_matrix(&((*preopt)->A), A_idxval, npred, N, nt);
 	SHOW_TIME("A_idxval");
 
+	GMRFLib_idxval_to_matrix(&((*preopt)->A), A_idxval, npred, N, nt);
+	SHOW_TIME("A_idxval to matrix");
+
 	// need also At_.. below, if (pA)
 	At_idxval = GMRFLib_idxval_ncreate_x(N, nf + nbeta, nt);
 	if (0) {
@@ -679,6 +681,7 @@ int GMRFLib_preopt_init(GMRFLib_preopt_tp **preopt, int npred, int nf, int **c,
 	GMRFLib_ged_build(&g, ged);
 	GMRFLib_ged_free(ged);
 	assert(g->n == gen_len_At);
+
 	SHOW_TIME("like graph-2");
 
 	AtA_idxval = Calloc(gen_len_At, GMRFLib_idxval_tp **);
@@ -710,6 +713,7 @@ int GMRFLib_preopt_init(GMRFLib_preopt_tp **preopt, int npred, int nf, int **c,
 			}
 		}
 	}
+
 	SHOW_TIME("AtA_idxval");
 
 	if (debug_detailed) {
@@ -734,6 +738,7 @@ int GMRFLib_preopt_init(GMRFLib_preopt_tp **preopt, int npred, int nf, int **c,
 			}
 		}
 	}
+
 #pragma omp parallel for num_threads(nt)
 	for (int i = 0; i < g->n; i++) {
 		GMRFLib_idxval_prepare(AtA_idxval[i], 1 + g->lnnbs[i], 1);
@@ -767,10 +772,13 @@ int GMRFLib_preopt_init(GMRFLib_preopt_tp **preopt, int npred, int nf, int **c,
 	GMRFLib_graph_tp *g_arr[2];
 	g_arr[0] = (*preopt)->latent_graph;
 	g_arr[1] = (*preopt)->like_graph;
-	GMRFLib_graph_union(&((*preopt)->preopt_graph), g_arr, 2);
 
 	SHOW_TIME("admin-2");
 
+	GMRFLib_graph_union(&((*preopt)->preopt_graph), g_arr, 2);
+
+	SHOW_TIME("graph-union");
+
 #if !defined(WINDOWS)
 	if (getenv("INLA_INTERNAL_DUMP_GRAPH")) {
 		static int count = 0;