diff --git a/src/worktree_manager.rs b/src/worktree_manager.rs
index 643aae7..534aaac 100644
--- a/src/worktree_manager.rs
+++ b/src/worktree_manager.rs
@@ -76,6 +76,19 @@ pub fn ensure_worktrees_in_gitignore(repo_path: &Path, worktree_dir: &Path) -> R
         if content.lines().any(|line| line.trim() == pattern) {
             return Ok(());
         }
+
+        let mut file = OpenOptions::new()
+            .append(true)
+            .open(&gitignore_path)
+            .context("Failed to open .gitignore")?;
+
+        if !content.is_empty() && !content.ends_with('\n') {
+            file.write_all(b"\n")
+                .context("Failed to write newline to .gitignore")?;
+        }
+
+        writeln!(file, "{}", pattern).context("Failed to write to .gitignore")?;
+        return Ok(());
     }
 
     let mut file = OpenOptions::new()
diff --git a/tests/which_test.rs b/tests/which_test.rs
index ad84d23..41db31e 100644
--- a/tests/which_test.rs
+++ b/tests/which_test.rs
@@ -119,6 +119,22 @@ fn test_ensure_worktrees_in_gitignore_appends_to_existing() {
     assert!(content.contains(".worktrees"));
 }
 
+#[test]
+fn test_ensure_worktrees_in_gitignore_adds_newline_when_missing() {
+    use wt::worktree_manager::ensure_worktrees_in_gitignore;
+
+    let repo = setup_git_repo();
+    let gitignore_path = repo.path().join(".gitignore");
+    let worktree_dir = repo.path().join(".worktrees");
+
+    fs::write(&gitignore_path, "node_modules").unwrap();
+
+    ensure_worktrees_in_gitignore(repo.path(), &worktree_dir).unwrap();
+
+    let content = fs::read_to_string(&gitignore_path).unwrap();
+    assert_eq!(content, "node_modules\n.worktrees\n");
+}
+
 #[test]
 fn test_ensure_worktrees_in_gitignore_idempotent() {
     use wt::worktree_manager::ensure_worktrees_in_gitignore;