diff --git a/CHANGELOG.md b/CHANGELOG.md
index be84a61..7225362 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Fixed
 
 - Fixed actor object JSON-LD validation errors.
+- Fixed activity JSON-LD validation errors.
 
 ## [1.13.1] - 2023-02-09
 
diff --git a/src/activitypub/types.rs b/src/activitypub/types.rs
index d3bd8b5..c4150bb 100644
--- a/src/activitypub/types.rs
+++ b/src/activitypub/types.rs
@@ -1,8 +1,15 @@
+use std::collections::HashMap;
+
 use chrono::{DateTime, Utc};
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
 
-use super::constants::{AP_CONTEXT, W3ID_DATA_INTEGRITY_CONTEXT};
+use super::constants::{
+    AP_CONTEXT,
+    MITRA_CONTEXT,
+    W3ID_DATA_INTEGRITY_CONTEXT,
+    W3ID_SECURITY_CONTEXT,
+};
 use super::vocabulary::HASHTAG;
 
 #[derive(Deserialize, Serialize)]
@@ -101,11 +108,24 @@ pub struct Object {
     pub url: Option<Value>,
 }
 
-pub type Context = [&'static str; 2];
+pub type Context = (
+    &'static str,
+    &'static str,
+    &'static str,
+    HashMap<&'static str, &'static str>,
+);
 
-pub const fn build_default_context() -> Context {
-    [
+pub fn build_default_context() -> Context {
+    (
         AP_CONTEXT,
+        W3ID_SECURITY_CONTEXT,
         W3ID_DATA_INTEGRITY_CONTEXT,
-    ]
+        HashMap::from([
+            ("proofValue", "sec:proofValue"),
+            ("proofPurpose", "sec:proofPurpose"),
+            ("verificationMethod", "sec:verificationMethod"),
+            ("mitra", MITRA_CONTEXT),
+            ("MitraJcsRsaSignature2022", "mitra:MitraJcsRsaSignature2022"),
+        ]),
+    )
 }