diff --git a/script/upstream/merge.ts b/script/upstream/merge.ts
index db3245c1c1d..e4ac18f7441 100644
--- a/script/upstream/merge.ts
+++ b/script/upstream/merge.ts
@@ -536,7 +536,7 @@ async function main() {
   const compatMessage = `refactor: kilo compat for ${targetVersion.tag}`
   if (prior) {
     const tree = await git.writeTree()
-    const commit = await git.createMergeCommit(tree, compatMessage, targetVersion.commit, prior.commit)
+    const commit = await git.createCommit(tree, compatMessage, prior.commit)
     await git.updateBranch(opencodeBranch, commit)
     await git.checkout(opencodeBranch)
   } else {
diff --git a/script/upstream/utils/git.test.ts b/script/upstream/utils/git.test.ts
index 5636241a2f7..999510bb42b 100644
--- a/script/upstream/utils/git.test.ts
+++ b/script/upstream/utils/git.test.ts
@@ -3,7 +3,7 @@ import { mkdtemp, rm } from "node:fs/promises"
 import { join } from "node:path"
 import { tmpdir } from "node:os"
 import { $ } from "bun"
-import { createMergeCommit, findLatestCompatCommit, getCommitHash, updateBranch, writeTree } from "./git"
+import { createCommit, findLatestCompatCommit, getCommitHash, getCommitParents, updateBranch, writeTree } from "./git"
 
 const cwd = process.cwd()
 let dir = ""
@@ -27,7 +27,7 @@ afterEach(async () => {
   await rm(dir, { recursive: true, force: true })
 })
 
-test("finds previous compatibility commit for transformed merge base", async () => {
+test("finds previous compatibility commit for transformed base", async () => {
   await Bun.write("brand.txt", "opencode A\n")
   const old = await commit("release: v1.0.0")
 
@@ -47,9 +47,10 @@ test("finds previous compatibility commit for transformed merge base", async ()
   await Bun.write("brand.txt", "kilo B\n")
   await $`git add -A`.quiet()
   const tree = await writeTree()
-  const next = await createMergeCommit(tree, "refactor: kilo compat for v1.0.1", target, prior)
+  const next = await createCommit(tree, "refactor: kilo compat for v1.0.1", prior)
   await updateBranch("opencode-v1.0.1", next)
 
   const base = (await $`git merge-base main opencode-v1.0.1`.text()).trim()
   expect(base).toBe(prior)
+  expect(await getCommitParents(next)).toEqual([prior])
 })
diff --git a/script/upstream/utils/git.ts b/script/upstream/utils/git.ts
index 4e9ccea8197..b25212de02a 100644
--- a/script/upstream/utils/git.ts
+++ b/script/upstream/utils/git.ts
@@ -196,8 +196,8 @@ export async function writeTree(): Promise<string> {
   return result.trim()
 }
 
-export async function createMergeCommit(tree: string, message: string, first: string, second: string): Promise<string> {
-  const result = await $`git commit-tree ${tree} -p ${first} -p ${second} -m ${message}`.text()
+export async function createCommit(tree: string, message: string, parent: string): Promise<string> {
+  const result = await $`git commit-tree ${tree} -p ${parent} -m ${message}`.text()
   return result.trim()
 }