diff --git a/crates/prek/src/hooks/pre_commit_hooks/no_commit_to_branch.rs b/crates/prek/src/hooks/pre_commit_hooks/no_commit_to_branch.rs
index 5eb2c80f3..1f38f1c56 100644
--- a/crates/prek/src/hooks/pre_commit_hooks/no_commit_to_branch.rs
+++ b/crates/prek/src/hooks/pre_commit_hooks/no_commit_to_branch.rs
@@ -1,16 +1,48 @@
+use std::sync::LazyLock;
+
 use clap::Parser;
 use fancy_regex::Regex;
 
-use crate::git::git_cmd;
+use crate::git::{GIT, git_cmd};
 use crate::hook::Hook;
 use anyhow::{Context, Result};
 
+/// Build the default protected branch list from a base set plus an optional detected branch.
+fn default_branches_with(detected: Option<&str>) -> Vec<String> {
+    let mut branches = vec!["main".to_string(), "master".to_string()];
+    if let Some(branch) = detected {
+        let trimmed = branch.trim().trim_start_matches("origin/");
+        if !trimmed.is_empty() && !branches.iter().any(|b| b == trimmed) {
+            branches.push(trimmed.to_string());
+        }
+    }
+    branches
+}
+
+/// Default protected branches: "main", "master", and the repo's default branch pointed to
+/// by `origin/HEAD` (if detectable and not already covered by main+master)
+static DEFAULT_BRANCHES: LazyLock<Vec<String>> = LazyLock::new(|| {
+    let detected = GIT.as_ref().ok().and_then(|git| {
+        let output = std::process::Command::new(git)
+            .arg("symbolic-ref")
+            .arg("--short")
+            .arg("origin/HEAD")
+            .output()
+            .ok()?;
+        output
+            .status
+            .success()
+            .then(|| String::from_utf8_lossy(&output.stdout).into_owned())
+    });
+    default_branches_with(detected.as_deref())
+});
+
 #[derive(Parser)]
 #[command(disable_help_subcommand = true)]
 #[command(disable_version_flag = true)]
 #[command(disable_help_flag = true)]
 struct Args {
-    #[arg(short, long = "branch", default_values = &["main", "master"])]
+    #[arg(short, long = "branch", default_values_t = DEFAULT_BRANCHES.clone())]
     branches: Vec<String>,
     #[arg(short, long = "pattern")]
     patterns: Vec<String>,
@@ -64,3 +96,106 @@ pub(crate) async fn no_commit_to_branch(hook: &Hook) -> Result<(i32, Vec<u8>)> {
         Ok((0, Vec::new()))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn parse_args(args: &[&str]) -> Args {
+        Args::try_parse_from(std::iter::once("no-commit-to-branch").chain(args.iter().copied()))
+            .unwrap()
+    }
+
+    #[test]
+    fn defaults_include_main_and_master() {
+        let args = parse_args(&[]);
+        assert!(args.branches.contains(&"main".to_string()));
+        assert!(args.branches.contains(&"master".to_string()));
+    }
+
+    #[test]
+    fn explicit_branches_override_defaults() {
+        let args = parse_args(&["-b", "develop", "-b", "release"]);
+        assert_eq!(args.branches, vec!["develop", "release"]);
+        assert!(!args.branches.contains(&"main".to_string()));
+    }
+
+    #[test]
+    fn check_protected_matches_exact_branch() {
+        let args = parse_args(&["-b", "main"]);
+        assert!(args.check_protected("main").unwrap());
+        assert!(!args.check_protected("main-feature").unwrap());
+    }
+
+    #[test]
+    fn check_protected_no_match_returns_false() {
+        let args = parse_args(&["-b", "main"]);
+        assert!(!args.check_protected("develop").unwrap());
+    }
+
+    #[test]
+    fn check_protected_with_pattern() {
+        let args = parse_args(&["-b", "main", "-p", "^release/.*$"]);
+        assert!(args.check_protected("release/1.0").unwrap());
+        assert!(!args.check_protected("feature/release/1.0").unwrap());
+    }
+
+    #[test]
+    fn check_protected_pattern_without_branch_match() {
+        let args = parse_args(&["-b", "nope", "-p", "^hotfix/"]);
+        assert!(!args.check_protected("main").unwrap());
+        assert!(args.check_protected("hotfix/urgent").unwrap());
+    }
+
+    #[test]
+    fn check_protected_no_patterns_ignores_regex() {
+        let args = parse_args(&["-b", "main"]);
+        // No patterns set, so only exact branch match applies
+        assert!(!args.check_protected("anything-else").unwrap());
+    }
+
+    #[test]
+    fn invalid_regex_pattern_returns_error() {
+        let args = parse_args(&["-b", "main", "-p", "([invalid"]);
+        assert!(args.check_protected("some-branch").is_err());
+    }
+
+    #[test]
+    fn default_branches_includes_detected_non_standard_branch() {
+        let branches = default_branches_with(Some("origin/develop"));
+        assert!(branches.contains(&"main".to_string()));
+        assert!(branches.contains(&"master".to_string()));
+        assert!(branches.contains(&"develop".to_string()));
+    }
+
+    #[test]
+    fn default_branches_does_not_duplicate_main() {
+        let branches = default_branches_with(Some("origin/main"));
+        assert_eq!(branches.iter().filter(|b| *b == "main").count(), 1);
+    }
+
+    #[test]
+    fn default_branches_does_not_duplicate_master() {
+        let branches = default_branches_with(Some("origin/master"));
+        assert_eq!(branches.iter().filter(|b| *b == "master").count(), 1);
+    }
+
+    #[test]
+    fn default_branches_handles_none_detected() {
+        let branches = default_branches_with(None);
+        assert_eq!(branches, vec!["main", "master"]);
+    }
+
+    #[test]
+    fn default_branches_ignores_empty_detected() {
+        let branches = default_branches_with(Some(""));
+        assert_eq!(branches, vec!["main", "master"]);
+    }
+
+    #[test]
+    fn default_branches_strips_origin_prefix() {
+        let branches = default_branches_with(Some("origin/production"));
+        assert!(branches.contains(&"production".to_string()));
+        assert!(!branches.iter().any(|b| b.contains("origin/")));
+    }
+}
diff --git a/docs/builtin.md b/docs/builtin.md
index 7be480514..a8c86a549 100644
--- a/docs/builtin.md
+++ b/docs/builtin.md
@@ -478,7 +478,7 @@ Protects specific branches from direct commits.
 
 **Supported arguments** (compatible with `pre-commit-hooks`):
 
-- `-b`, `--branch <branch>` (repeatable, default: `main`, `master`)
+- `-b`, `--branch <branch>` (repeatable, default: `main`, `master`, and the branch pointed to by `origin/HEAD`)
 - `-p`, `--pattern <regex>` (repeatable)
 
 **Caveats**