diff --git a/ci-broker.md b/ci-broker.md
index 48b79e3c..bea74d56 100644
--- a/ci-broker.md
+++ b/ci-broker.md
@@ -1194,6 +1194,42 @@ triggers:
 ~~~
 
 
+## Filter predicate `DefaultBranch`
+
+_Want:_ We can allow an event if the event refers to the default
+branch.
+
+_Why:_ This is so that the user doesn't need to spell out the name
+explicitly.
+
+~~~scenario
+given a Radicle node, with CI configured with broker.yaml and adapter dummy.sh
+given a Git repository xyzzy in the Radicle node
+
+given file config.yaml from filter-defaultbranch.yaml
+
+when I run cibtool --db ci-broker.db event add --repo xyzzy --ref main --commit HEAD --kind branch-created
+when I run cibtool --db ci-broker.db event add --repo xyzzy --ref oksa --commit HEAD --kind branch-created
+
+when I run ./env.sh cib --config config.yaml queued
+
+when I run cibtool --db ci-broker.db run list --json
+then stdout contains "main"
+then stdout doesn't contain "oksa"
+~~~
+
+~~~{#filter-defaultbranch.yaml .file .json}
+db: ci-broker.db
+adapters:
+  default:
+    command: ./adapter.sh
+triggers:
+  - adapter: default
+    filters:
+      - !DefaultBranch
+~~~
+
+
 # Acceptance criteria for test tooling
 
 The event synthesizer is a helper to feed the CI broker node events in
diff --git a/src/filter.rs b/src/filter.rs
index f2149124..b860dcdd 100644
--- a/src/filter.rs
+++ b/src/filter.rs
@@ -2,7 +2,13 @@ use std::path::{Path, PathBuf};
 
 use serde::{Deserialize, Serialize};
 
-use radicle::{cob::patch::PatchId, git::RefString, node::NodeId, prelude::RepoId};
+use radicle::{
+    cob::patch::PatchId,
+    git::RefString,
+    node::NodeId,
+    prelude::{Profile, RepoId},
+    storage::git::Repository,
+};
 use radicle_git_ext::Oid;
 
 use crate::{
@@ -49,6 +55,9 @@ pub enum EventFilter {
     /// Event is for a specific branch.
     Branch(RefString),
 
+    /// Event if for the default branch for the repository.
+    DefaultBranch,
+
     /// Branch was created.
     BranchCreated,
 
@@ -113,6 +122,7 @@ impl EventFilter {
                 Self::Node(wantedc) => from_node == wantedc,
                 Self::Repository(wanted) => repo == wanted,
                 Self::Branch(wanted) => branch == wanted,
+                Self::DefaultBranch => is_default_branch(repo, branch),
                 Self::BranchCreated => true,
                 _ => false,
             },
@@ -125,6 +135,7 @@ impl EventFilter {
                 Self::Node(wanted) => from_node == wanted,
                 Self::Repository(wanted) => repo == wanted,
                 Self::Branch(wanted) => branch == wanted,
+                Self::DefaultBranch => is_default_branch(repo, branch),
                 Self::BranchUpdated => true,
                 _ => false,
             },
@@ -137,6 +148,7 @@ impl EventFilter {
                 Self::Node(wanted) => from_node == wanted,
                 Self::Repository(wanted) => repo == wanted,
                 Self::Branch(wanted) => branch == wanted,
+                Self::DefaultBranch => is_default_branch(repo, branch),
                 Self::BranchDeleted => true,
                 _ => false,
             },
@@ -176,6 +188,39 @@ impl EventFilter {
     }
 }
 
+fn is_default_branch(repo_id: &RepoId, wanted: &str) -> bool {
+    let res = get_default_branch(repo_id);
+    logger::debug2(format!("is_default_branch: res={res:?}"));
+    if let Ok(actual) = res {
+        logger::debug2(format!(
+            "is_default_branch: actual={actual} wanted={wanted}"
+        ));
+        actual == wanted
+    } else {
+        logger::debug("is_default_branch: could not get actual");
+        false
+    }
+}
+
+fn get_default_branch(repo_id: &RepoId) -> Result<String, Box<dyn std::error::Error>> {
+    let profile = Profile::load()?;
+    logger::debug("loaded profile");
+    let path = profile.storage.path().join(repo_id.canonical());
+    logger::debug2(format!("path={}", path.display()));
+    let repo = Repository::open(path, *repo_id)?;
+    logger::debug("loaded repo");
+    let proj = repo.project()?;
+    logger::debug("loaded project");
+
+    let def = format!(
+        "{}/refs/heads/{}",
+        profile.id().to_namespace(),
+        proj.default_branch()
+    );
+
+    Ok(def)
+}
+
 #[derive(Deserialize)]
 struct Filters {
     filters: Vec<EventFilter>,