diff --git a/commit-graph.c b/commit-graph.c
index b3f7c3bbcb3..2790f70d113 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -1446,27 +1446,24 @@ static void close_reachable(struct write_commit_graph_context *ctx)
 	stop_progress(&ctx->progress);
 }
 
-static void compute_generation_numbers(struct write_commit_graph_context *ctx)
+static void compute_topological_levels(struct write_commit_graph_context *ctx)
 {
 	int i;
 	struct commit_list *list = NULL;
 
 	if (ctx->report_progress)
 		ctx->progress = start_delayed_progress(
-					_("Computing commit graph generation numbers"),
+					_("Computing commit graph topological levels"),
 					ctx->commits.nr);
 	for (i = 0; i < ctx->commits.nr; i++) {
 		struct commit *c = ctx->commits.list[i];
 		uint32_t level;
-		timestamp_t corrected_commit_date;
 
 		repo_parse_commit(ctx->r, c);
 		level = *topo_level_slab_at(ctx->topo_levels, c);
-		corrected_commit_date = commit_graph_data_at(c)->generation;
 
 		display_progress(ctx->progress, i + 1);
-		if (level != GENERATION_NUMBER_ZERO &&
-		    corrected_commit_date != GENERATION_NUMBER_ZERO)
+		if (level != GENERATION_NUMBER_ZERO)
 			continue;
 
 		commit_list_insert(c, &list);
@@ -1475,15 +1472,12 @@ static void compute_generation_numbers(struct write_commit_graph_context *ctx)
 			struct commit_list *parent;
 			int all_parents_computed = 1;
 			uint32_t max_level = 0;
-			timestamp_t max_corrected_commit_date = 0;
 
 			for (parent = current->parents; parent; parent = parent->next) {
 				repo_parse_commit(ctx->r, parent->item);
 				level = *topo_level_slab_at(ctx->topo_levels, parent->item);
-				corrected_commit_date = commit_graph_data_at(parent->item)->generation;
 
-				if (level == GENERATION_NUMBER_ZERO ||
-				    corrected_commit_date == GENERATION_NUMBER_ZERO) {
+				if (level == GENERATION_NUMBER_ZERO) {
 					all_parents_computed = 0;
 					commit_list_insert(parent->item, &list);
 					break;
@@ -1491,9 +1485,6 @@ static void compute_generation_numbers(struct write_commit_graph_context *ctx)
 
 				if (level > max_level)
 					max_level = level;
-
-				if (corrected_commit_date > max_corrected_commit_date)
-					max_corrected_commit_date = corrected_commit_date;
 			}
 
 			if (all_parents_computed) {
@@ -1502,6 +1493,55 @@ static void compute_generation_numbers(struct write_commit_graph_context *ctx)
 				if (max_level > GENERATION_NUMBER_V1_MAX - 1)
 					max_level = GENERATION_NUMBER_V1_MAX - 1;
 				*topo_level_slab_at(ctx->topo_levels, current) = max_level + 1;
+			}
+		}
+	}
+	stop_progress(&ctx->progress);
+}
+
+static void compute_generation_numbers(struct write_commit_graph_context *ctx)
+{
+	int i;
+	struct commit_list *list = NULL;
+
+	if (ctx->report_progress)
+		ctx->progress = start_delayed_progress(
+					_("Computing commit graph generation numbers"),
+					ctx->commits.nr);
+	for (i = 0; i < ctx->commits.nr; i++) {
+		struct commit *c = ctx->commits.list[i];
+		timestamp_t corrected_commit_date;
+
+		repo_parse_commit(ctx->r, c);
+		corrected_commit_date = commit_graph_data_at(c)->generation;
+
+		display_progress(ctx->progress, i + 1);
+		if (corrected_commit_date != GENERATION_NUMBER_ZERO)
+			continue;
+
+		commit_list_insert(c, &list);
+		while (list) {
+			struct commit *current = list->item;
+			struct commit_list *parent;
+			int all_parents_computed = 1;
+			timestamp_t max_corrected_commit_date = 0;
+
+			for (parent = current->parents; parent; parent = parent->next) {
+				repo_parse_commit(ctx->r, parent->item);
+				corrected_commit_date = commit_graph_data_at(parent->item)->generation;
+
+				if (corrected_commit_date == GENERATION_NUMBER_ZERO) {
+					all_parents_computed = 0;
+					commit_list_insert(parent->item, &list);
+					break;
+				}
+
+				if (corrected_commit_date > max_corrected_commit_date)
+					max_corrected_commit_date = corrected_commit_date;
+			}
+
+			if (all_parents_computed) {
+				pop_commit(&list);
 
 				if (current->date && current->date > max_corrected_commit_date)
 					max_corrected_commit_date = current->date - 1;
@@ -2401,7 +2441,9 @@ int write_commit_graph(struct object_directory *odb,
 
 	validate_mixed_generation_chain(ctx->r->objects->commit_graph);
 
-	compute_generation_numbers(ctx);
+	compute_topological_levels(ctx);
+	if (ctx->write_generation_data)
+		compute_generation_numbers(ctx);
 
 	if (ctx->changed_paths)
 		compute_bloom_filters(ctx);
