diff --git a/changelogs/unreleased/pks-go-user-merge-branch-reversed-parents.yml b/changelogs/unreleased/pks-go-user-merge-branch-reversed-parents.yml
new file mode 100644
index 0000000000000000000000000000000000000000..6a59a8ee94798c7cc659229f847e6aa145e73ee0
--- /dev/null
+++ b/changelogs/unreleased/pks-go-user-merge-branch-reversed-parents.yml
@@ -0,0 +1,5 @@
+---
+title: 'operations: Fix wrong ordering of merge parents for UserMergeBranch'
+merge_request: 2868
+author:
+type: fixed
diff --git a/internal/gitaly/service/operations/merge.go b/internal/gitaly/service/operations/merge.go
index 64c6ad2764430feaadd5ef31b49789b64b24bd36..93fd778294770c3ccc5dfdeee42a50b71c557361 100644
--- a/internal/gitaly/service/operations/merge.go
+++ b/internal/gitaly/service/operations/merge.go
@@ -123,8 +123,8 @@ func (s *Server) userMergeBranch(stream gitalypb.OperationService_UserMergeBranc
 		AuthorName: string(firstRequest.User.Name),
 		AuthorMail: string(firstRequest.User.Email),
 		Message:    string(firstRequest.Message),
-		Ours:       firstRequest.CommitId,
-		Theirs:     revision,
+		Ours:       revision,
+		Theirs:     firstRequest.CommitId,
 	}.Run(ctx, s.cfg)
 	if err != nil {
 		if errors.Is(err, git2go.ErrInvalidArgument) {
diff --git a/internal/gitaly/service/operations/merge_test.go b/internal/gitaly/service/operations/merge_test.go
index e1e0a7759208bc679c1ec0844df6995b0530ed99..c9b467fb11517ff8f4173056a504e5e5b73b6872 100644
--- a/internal/gitaly/service/operations/merge_test.go
+++ b/internal/gitaly/service/operations/merge_test.go
@@ -104,8 +104,7 @@ func testSuccessfulMerge(t *testing.T, ctx context.Context) {
 
 	require.Equal(t, gitalypb.OperationBranchUpdate{CommitId: commit.Id}, *(secondResponse.BranchUpdate))
 
-	require.Contains(t, commit.ParentIds, mergeBranchHeadBefore, "merge parents must include previous HEAD of branch")
-	require.Contains(t, commit.ParentIds, commitToMerge, "merge parents must include commit to merge")
+	require.Equal(t, commit.ParentIds, []string{mergeBranchHeadBefore, commitToMerge})
 
 	require.True(t, strings.HasPrefix(string(commit.Body), mergeCommitMessage), "expected %q to start with %q", commit.Body, mergeCommitMessage)