diff --git a/commit-graph.c b/commit-graph.c
index c91e6f0fb82158..1aaf02879b9d73 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -1629,7 +1629,7 @@ static void sort_and_scan_merged_commits(struct write_commit_graph_context *ctx)
 				num_parents++;
 
 			if (num_parents > 2)
-				ctx->num_extra_edges += num_parents - 2;
+				ctx->num_extra_edges += num_parents - 1;
 		}
 	}
 
diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
index 03f45a1ed9023c..99f4ef4c19dff0 100755
--- a/t/t5324-split-commit-graph.sh
+++ b/t/t5324-split-commit-graph.sh
@@ -319,7 +319,9 @@ test_expect_success 'add octopus merge' '
 	git merge commits/3 commits/4 &&
 	git branch merge/octopus &&
 	git commit-graph write --reachable --split &&
-	git commit-graph verify &&
+	git commit-graph verify 2>err &&
+	test_line_count = 3 err &&
+	test_i18ngrep ! warning err &&
 	test_line_count = 3 $graphdir/commit-graph-chain
 '