diff --git a/internal/config/config.go b/internal/config/config.go
index aed135de0c..70953b97a9 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -95,7 +95,7 @@ type Config struct {
 	APISource string
 
 	// APISourceDepth controls the depth of the repository closing **IF**
-	// APISource is a github repository and it is cloned.
+	// APISource is a GitHub repository, and it is cloned.
 	APISourceDepth int
 
 	// Branch is the remote branch of the language repository to use.
diff --git a/internal/librarian/command.go b/internal/librarian/command.go
index f6ba865d97..769fc44333 100644
--- a/internal/librarian/command.go
+++ b/internal/librarian/command.go
@@ -92,8 +92,8 @@ type commandRunner struct {
 	librarianConfig *config.LibrarianConfig
 	ghClient        GitHubClient
 	containerClient ContainerClient
-	workRoot        string
 	image           string
+	workRoot        string
 }
 
 const defaultAPISourceBranch = "master"
diff --git a/internal/librarian/generate.go b/internal/librarian/generate.go
index 7a166698e7..f21c43cb79 100644
--- a/internal/librarian/generate.go
+++ b/internal/librarian/generate.go
@@ -57,6 +57,7 @@ func newGenerateRunner(cfg *config.Config) (*generateRunner, error) {
 	return &generateRunner{
 		api:             cfg.API,
 		apiSource:       cfg.APISource,
+		branch:          cfg.Branch,
 		build:           cfg.Build,
 		commit:          cfg.Commit,
 		containerClient: runner.containerClient,
diff --git a/internal/librarian/generate_test.go b/internal/librarian/generate_test.go
index b8f1866c6b..e27550c3da 100644
--- a/internal/librarian/generate_test.go
+++ b/internal/librarian/generate_test.go
@@ -381,15 +381,17 @@ func TestRunConfigureCommand(t *testing.T) {
 func TestNewGenerateRunner(t *testing.T) {
 	t.Parallel()
 	for _, test := range []struct {
-		name    string
-		cfg     *config.Config
-		wantErr bool
+		name       string
+		cfg        *config.Config
+		wantErr    bool
+		wantErrMsg string
 	}{
 		{
 			name: "valid config",
 			cfg: &config.Config{
 				API:         "some/api",
 				APISource:   newTestGitRepo(t).GetDir(),
+				Branch:      "test-branch",
 				Repo:        newTestGitRepo(t).GetDir(),
 				WorkRoot:    t.TempDir(),
 				Image:       "gcr.io/test/test-image",
@@ -406,13 +408,15 @@ func TestNewGenerateRunner(t *testing.T) {
 				Image:       "gcr.io/test/test-image",
 				CommandName: generateCmdName,
 			},
-			wantErr: true,
+			wantErr:    true,
+			wantErrMsg: "repository does not exist",
 		},
 		{
 			name: "missing image",
 			cfg: &config.Config{
 				API:         "some/api",
 				APISource:   t.TempDir(),
+				Branch:      "test-branch",
 				Repo:        "https://github.com/googleapis/librarian.git",
 				WorkRoot:    t.TempDir(),
 				CommandName: generateCmdName,
@@ -424,6 +428,7 @@ func TestNewGenerateRunner(t *testing.T) {
 			cfg: &config.Config{
 				API:         "some/api",
 				APISource:   newTestGitRepo(t).GetDir(),
+				Branch:      "test-branch",
 				Repo:        newTestGitRepo(t).GetDir(),
 				WorkRoot:    t.TempDir(),
 				Image:       "gcr.io/test/test-image",
@@ -437,6 +442,7 @@ func TestNewGenerateRunner(t *testing.T) {
 				API:            "some/api",
 				APISource:      "https://github.com/googleapis/googleapis", // This will trigger the clone of googleapis
 				APISourceDepth: 1,
+				Branch:         "test-branch",
 				Repo:           newTestGitRepo(t).GetDir(),
 				WorkRoot:       t.TempDir(),
 				Image:          "gcr.io/test/test-image",
@@ -454,13 +460,15 @@ func TestNewGenerateRunner(t *testing.T) {
 				Image:          "gcr.io/test/test-image",
 				CommandName:    generateCmdName,
 			},
-			wantErr: true,
+			wantErr:    true,
+			wantErrMsg: "repo must be specified",
 		},
 		{
 			name: "valid config with local repo",
 			cfg: &config.Config{
 				API:         "some/api",
 				APISource:   newTestGitRepo(t).GetDir(),
+				Branch:      "test-branch",
 				Repo:        newTestGitRepo(t).GetDir(),
 				WorkRoot:    t.TempDir(),
 				Image:       "gcr.io/test/test-image",
@@ -500,12 +508,26 @@ func TestNewGenerateRunner(t *testing.T) {
 			}
 
 			r, err := newGenerateRunner(test.cfg)
-			if (err != nil) != test.wantErr {
-				t.Errorf("newGenerateRunner() error = %v, wantErr %v", err, test.wantErr)
-			}
 			if test.wantErr {
+				if err == nil {
+					t.Fatalf("newGenerateRunner() error = %v, wantErr %v", err, test.wantErr)
+				}
+
+				if !strings.Contains(err.Error(), test.wantErrMsg) {
+					t.Fatalf("want error message: %s, got: %s", test.wantErrMsg, err.Error())
+				}
+
 				return
 			}
+
+			if err != nil {
+				t.Fatalf("newGenerateRunner() got error: %v", err)
+			}
+
+			if r.branch == "" {
+				t.Errorf("newGenerateRunner() branch is not set")
+			}
+
 			if r.ghClient == nil {
 				t.Errorf("newGenerateRunner() ghClient is nil")
 			}