diff --git a/integration-tests/set_remote_test.go b/integration-tests/set_remote_test.go
new file mode 100644
index 000000000..efeef393c
--- /dev/null
+++ b/integration-tests/set_remote_test.go
@@ -0,0 +1,141 @@
+package tests
+
+import (
+	"net/http/httptest"
+	"net/url"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/upsun/cli/pkg/mockapi"
+)
+
+// initGitRepo creates an empty Git repository in a temporary directory and
+// returns its path.
+func initGitRepo(t *testing.T) string {
+	t.Helper()
+	dir := t.TempDir()
+	for _, args := range [][]string{
+		{"init", "--quiet", "--initial-branch=main"},
+		{"config", "user.email", "test@example.com"},
+		{"config", "user.name", "Test"},
+		{"config", "commit.gpgsign", "false"},
+	} {
+		cmd := exec.Command("git", args...)
+		cmd.Dir = dir
+		out, err := cmd.CombinedOutput()
+		require.NoError(t, err, "git %v failed: %s", args, out)
+	}
+	return dir
+}
+
+func gitConfig(t *testing.T, dir, key string) string {
+	t.Helper()
+	out, err := exec.Command("git", "-C", dir, "config", "--get", key).Output()
+	if err != nil {
+		var ee *exec.ExitError
+		if ok := assert.ErrorAs(t, err, &ee); ok && ee.ExitCode() == 1 {
+			return ""
+		}
+		require.NoError(t, err)
+	}
+	return string(out)
+}
+
+func TestProjectSetRemote(t *testing.T) {
+	authServer := mockapi.NewAuthServer(t)
+	defer authServer.Close()
+
+	apiHandler := mockapi.NewHandler(t)
+
+	projectID := mockapi.ProjectID()
+	gitURL := "test-user@git.cli-tests.example.com:" + projectID + ".git"
+	apiHandler.SetProjects([]*mockapi.Project{{
+		ID:            projectID,
+		Title:         "Set Remote Test",
+		Region:        "test-region",
+		DefaultBranch: "main",
+		Repository:    mockapi.ProjectRepository{URL: gitURL},
+		Links:         mockapi.MakeHALLinks("self=/projects/" + url.PathEscape(projectID)),
+	}})
+
+	apiServer := httptest.NewServer(apiHandler)
+	defer apiServer.Close()
+
+	t.Run("with project ID in fresh git repo", func(t *testing.T) {
+		// Regression test: the customer-reported bug was that running
+		// "set-remote PROJECT_ID" in a fresh Git checkout (no .platform/local
+		// config) failed with RootNotFoundException, because the unified
+		// Selector ignored the positional argument and tried to detect a
+		// current project from disk.
+		repo := initGitRepo(t)
+		f := newCommandFactory(t, apiServer.URL, authServer.URL)
+		f.dir = repo
+
+		_, stdErr, err := f.RunCombinedOutput("set-remote", projectID)
+		require.NoError(t, err, "stderr: %s", stdErr)
+		assert.Contains(t, stdErr, "Setting the remote project for this repository to:")
+		assert.Contains(t, stdErr, projectID)
+		assert.NotContains(t, stdErr, "RootNotFoundException")
+		assert.NotContains(t, stdErr, "Could not determine the current project")
+
+		configFile := filepath.Join(repo, ".platform", "local", "project.yaml")
+		body, readErr := os.ReadFile(configFile)
+		require.NoError(t, readErr)
+		assert.Contains(t, string(body), "id: "+projectID)
+
+		assert.Equal(t, gitURL+"\n", gitConfig(t, repo, "remote.platform-test.url"))
+	})
+
+	t.Run("with unknown project ID", func(t *testing.T) {
+		repo := initGitRepo(t)
+		f := newCommandFactory(t, apiServer.URL, authServer.URL)
+		f.dir = repo
+
+		_, stdErr, err := f.RunCombinedOutput("set-remote", "nonexistent")
+		ee := &exec.ExitError{}
+		require.ErrorAs(t, err, &ee)
+		assert.Equal(t, 1, ee.ExitCode())
+		assert.Contains(t, stdErr, "Project not found")
+
+		_, statErr := os.Stat(filepath.Join(repo, ".platform"))
+		assert.True(t, os.IsNotExist(statErr), "no project config should be written on failure")
+	})
+
+	t.Run("outside a git repository", func(t *testing.T) {
+		f := newCommandFactory(t, apiServer.URL, authServer.URL)
+		f.dir = t.TempDir()
+
+		_, stdErr, err := f.RunCombinedOutput("set-remote", projectID)
+		ee := &exec.ExitError{}
+		require.ErrorAs(t, err, &ee)
+		assert.Equal(t, 1, ee.ExitCode())
+		assert.Contains(t, stdErr, "No Git repository found")
+	})
+
+	t.Run("unset when nothing is mapped", func(t *testing.T) {
+		repo := initGitRepo(t)
+		f := newCommandFactory(t, apiServer.URL, authServer.URL)
+		f.dir = repo
+
+		_, stdErr, err := f.RunCombinedOutput("set-remote", "-")
+		require.NoError(t, err, "stderr: %s", stdErr)
+		assert.Contains(t, stdErr, "This repository is not mapped to a remote project.")
+	})
+
+	t.Run("without project ID in non-interactive mode", func(t *testing.T) {
+		repo := initGitRepo(t)
+		f := newCommandFactory(t, apiServer.URL, authServer.URL)
+		f.dir = repo
+
+		_, stdErr, err := f.RunCombinedOutput("set-remote")
+		ee := &exec.ExitError{}
+		require.ErrorAs(t, err, &ee)
+		assert.NotEqual(t, 0, ee.ExitCode())
+		assert.Contains(t, stdErr, "Could not determine the current project")
+	})
+}
diff --git a/integration-tests/tests.go b/integration-tests/tests.go
index f63335bf1..f049dac03 100644
--- a/integration-tests/tests.go
+++ b/integration-tests/tests.go
@@ -61,6 +61,7 @@ type cmdFactory struct {
 	apiURL   string
 	authURL  string
 	extraEnv []string
+	dir      string
 }
 
 func newCommandFactory(t *testing.T, apiURL, authURL string) *cmdFactory {
@@ -94,7 +95,10 @@ func (f *cmdFactory) RunCombinedOutput(args ...string) (stdOut, stdErr string, e
 func (f *cmdFactory) buildCommand(args ...string) *exec.Cmd {
 	cmd := exec.Command(getCommandName(f.t), args...) //nolint:gosec
 	cmd.Env = testEnv()
-	cmd.Dir = os.TempDir()
+	cmd.Dir = f.dir
+	if cmd.Dir == "" {
+		cmd.Dir = os.TempDir()
+	}
 	if testing.Verbose() {
 		cmd.Stderr = os.Stderr
 	}
diff --git a/legacy/src/Command/Project/ProjectSetRemoteCommand.php b/legacy/src/Command/Project/ProjectSetRemoteCommand.php
index 39abd974f..d91cff754 100644
--- a/legacy/src/Command/Project/ProjectSetRemoteCommand.php
+++ b/legacy/src/Command/Project/ProjectSetRemoteCommand.php
@@ -38,17 +38,11 @@ protected function configure(): void
 
     protected function execute(InputInterface $input, OutputInterface $output): int
     {
-        $projectId = $input->getArgument('project');
-        $unset = false;
-        if ($projectId === '-') {
-            $unset = true;
-            $projectId = null;
-        }
-
-        if ($projectId) {
-            $identifier = $this->identifier;
-            $result = $identifier->identify($projectId);
-            $projectId = $result['projectId'];
+        $projectArg = $input->getArgument('project');
+        $unset = $projectArg === '-';
+        $projectId = null;
+        if (!$unset && is_string($projectArg) && $projectArg !== '') {
+            $projectId = $this->identifier->identify($projectArg)['projectId'];
         }
         $cwd = getcwd();
         if (!$cwd) {
@@ -123,13 +117,17 @@ protected function execute(InputInterface $input, OutputInterface $output): int
             $selectorConfig = null;
         }
 
-        $asking = $projectId === null;
-        $selection = $this->selector->getSelection($input, $selectorConfig);
-        if ($asking) {
+        if ($projectId !== null) {
+            $project = $this->api->getProject($projectId);
+            if (!$project) {
+                $this->stdErr->writeln(sprintf('Project not found: <error>%s</error>', $projectId));
+                return 1;
+            }
+        } else {
+            $selection = $this->selector->getSelection($input, $selectorConfig);
             $this->stdErr->writeln('');
+            $project = $selection->getProject();
         }
-
-        $project = $selection->getProject();
         if ($currentProject && $currentProject->id === $project->id) {
             $this->stdErr->writeln(sprintf(
                 'The remote project for this repository is already set as: %s',