diff --git a/Cargo.lock b/Cargo.lock
index 7502491..15c4468 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -567,9 +567,9 @@ checksum = "b35204fbdc0b3f4446b89fc1ac2cf84a8a68971995d0bf2e925ec7cd960f9cb3"
 
 [[package]]
 name = "caldata"
-version = "0.12.1"
+version = "0.13.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "55ae67018b0b95d01f20a5f6869810e83969baa94b2ff768de7f90a8a9e38efd"
+checksum = "b39dd55be55606179c8437278d2df04a0fcfdc2956edcc432b2d54413e3f1522"
 dependencies = [
  "chrono",
  "chrono-tz",
@@ -580,6 +580,7 @@ dependencies = [
  "regex",
  "rrule",
  "thiserror 2.0.18",
+ "vtimezones-rs",
 ]
 
 [[package]]
@@ -4952,9 +4953,9 @@ checksum = "0b928f33d975fc6ad9f86c8f283853ad26bdd5b10b7f1542aa2fa15e2289105a"
 
 [[package]]
 name = "vtimezones-rs"
-version = "0.2.0"
+version = "0.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f6728de8767c8dea44f41b88115a205ed23adc3302e1b4342be59d922934dae5"
+checksum = "cd57da82560fa7a80104c812a084968666133f57f386e4b0970932115dbf819a"
 dependencies = [
  "glob",
  "phf 0.12.1",
diff --git a/Cargo.toml b/Cargo.toml
index e2ff35f..02fd12d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -107,7 +107,7 @@ strum = "0.27"
 strum_macros = "0.27"
 serde_json = { version = "1.0", features = ["raw_value"] }
 sqlx-sqlite = { version = "0.8", features = ["bundled"] }
-caldata = { version = "0.12.1", features = ["chrono-tz"] }
+caldata = { version = "0.13.0", features = ["chrono-tz", "vtimezones-rs"] }
 toml = "0.9"
 tower = "0.5"
 tower-http = { version = "0.6", features = [
diff --git a/crates/caldav/src/calendar/service.rs b/crates/caldav/src/calendar/service.rs
index 2f35acc..8bda9a3 100644
--- a/crates/caldav/src/calendar/service.rs
+++ b/crates/caldav/src/calendar/service.rs
@@ -6,7 +6,7 @@ use crate::calendar::methods::report::route_report_calendar;
 use crate::calendar::resource::CalendarResource;
 use crate::calendar_object::CalendarObjectResourceService;
 use crate::calendar_object::resource::CalendarObjectResource;
-use crate::{CalDavPrincipalUri, Error};
+use crate::{CalDavConfig, CalDavPrincipalUri, Error};
 use async_trait::async_trait;
 use axum::Router;
 use axum::extract::Request;
@@ -23,6 +23,7 @@ use tower::Service;
 pub struct CalendarResourceService<C: CalendarStore, S: SubscriptionStore> {
     pub(crate) cal_store: Arc<C>,
     pub(crate) sub_store: Arc<S>,
+    pub(crate) config: Arc<CalDavConfig>,
 }
 
 impl<C: CalendarStore, S: SubscriptionStore> Clone for CalendarResourceService<C, S> {
@@ -30,15 +31,17 @@ impl<C: CalendarStore, S: SubscriptionStore> Clone for CalendarResourceService<C
         Self {
             cal_store: self.cal_store.clone(),
             sub_store: self.sub_store.clone(),
+            config: self.config.clone(),
         }
     }
 }
 
 impl<C: CalendarStore, S: SubscriptionStore> CalendarResourceService<C, S> {
-    pub const fn new(cal_store: Arc<C>, sub_store: Arc<S>) -> Self {
+    pub const fn new(cal_store: Arc<C>, sub_store: Arc<S>, config: Arc<CalDavConfig>) -> Self {
         Self {
             cal_store,
             sub_store,
+            config,
         }
     }
 }
@@ -112,7 +115,8 @@ impl<C: CalendarStore, S: SubscriptionStore> ResourceService for CalendarResourc
         Router::new()
             .nest(
                 "/{object_id}",
-                CalendarObjectResourceService::new(self.cal_store.clone()).axum_router(),
+                CalendarObjectResourceService::new(self.cal_store.clone(), self.config.clone())
+                    .axum_router(),
             )
             .route_service("/", self.axum_service())
     }
diff --git a/crates/caldav/src/calendar_object/methods.rs b/crates/caldav/src/calendar_object/methods.rs
index 873bc59..c75eced 100644
--- a/crates/caldav/src/calendar_object/methods.rs
+++ b/crates/caldav/src/calendar_object/methods.rs
@@ -5,6 +5,7 @@ use axum::body::Body;
 use axum::extract::{Path, State};
 use axum::response::{IntoResponse, Response};
 use axum_extra::TypedHeader;
+use caldata::parser::ParserOptions;
 use headers::{ContentType, ETag, HeaderMapExt, IfNoneMatch};
 use http::{HeaderMap, HeaderValue, Method, StatusCode};
 use rustical_ical::CalendarObject;
@@ -20,7 +21,10 @@ pub async fn get_event<C: CalendarStore>(
         calendar_id,
         object_id,
     }): Path<CalendarObjectPathComponents>,
-    State(CalendarObjectResourceService { cal_store }): State<CalendarObjectResourceService<C>>,
+    State(CalendarObjectResourceService {
+        cal_store,
+        config: _,
+    }): State<CalendarObjectResourceService<C>>,
     user: Principal,
     method: Method,
 ) -> Result<Response, Error> {
@@ -57,7 +61,9 @@ pub async fn put_event<C: CalendarStore>(
         calendar_id,
         object_id,
     }): Path<CalendarObjectPathComponents>,
-    State(CalendarObjectResourceService { cal_store }): State<CalendarObjectResourceService<C>>,
+    State(CalendarObjectResourceService { cal_store, config }): State<
+        CalendarObjectResourceService<C>,
+    >,
     user: Principal,
     mut if_none_match: Option<TypedHeader<IfNoneMatch>>,
     header_map: HeaderMap,
@@ -94,7 +100,12 @@ pub async fn put_event<C: CalendarStore>(
         true
     };
 
-    let object = match CalendarObject::from_ics(body.clone()) {
+    let object = match CalendarObject::import(
+        &body,
+        Some(ParserOptions {
+            rfc7809: config.rfc7809,
+        }),
+    ) {
         Ok(object) => object,
         Err(err) => {
             warn!("invalid calendar data:\n{body}");
diff --git a/crates/caldav/src/calendar_object/service.rs b/crates/caldav/src/calendar_object/service.rs
index 97f1516..7ed9819 100644
--- a/crates/caldav/src/calendar_object/service.rs
+++ b/crates/caldav/src/calendar_object/service.rs
@@ -1,5 +1,5 @@
 use crate::{
-    CalDavPrincipalUri, Error,
+    CalDavConfig, CalDavPrincipalUri, Error,
     calendar_object::{
         methods::{get_event, put_event},
         resource::CalendarObjectResource,
@@ -24,19 +24,21 @@ pub struct CalendarObjectPathComponents {
 
 pub struct CalendarObjectResourceService<C: CalendarStore> {
     pub(crate) cal_store: Arc<C>,
+    pub(crate) config: Arc<CalDavConfig>,
 }
 
 impl<C: CalendarStore> Clone for CalendarObjectResourceService<C> {
     fn clone(&self) -> Self {
         Self {
             cal_store: self.cal_store.clone(),
+            config: self.config.clone(),
         }
     }
 }
 
 impl<C: CalendarStore> CalendarObjectResourceService<C> {
-    pub const fn new(cal_store: Arc<C>) -> Self {
-        Self { cal_store }
+    pub const fn new(cal_store: Arc<C>, config: Arc<CalDavConfig>) -> Self {
+        Self { cal_store, config }
     }
 }
 
diff --git a/crates/caldav/src/lib.rs b/crates/caldav/src/lib.rs
index 991dfc8..e9551b2 100644
--- a/crates/caldav/src/lib.rs
+++ b/crates/caldav/src/lib.rs
@@ -8,6 +8,7 @@ use rustical_dav::resources::RootResourceService;
 use rustical_store::auth::middleware::AuthenticationLayer;
 use rustical_store::auth::{AuthenticationProvider, Principal};
 use rustical_store::{CalendarStore, SubscriptionStore};
+use serde::{Deserialize, Serialize};
 use std::sync::Arc;
 
 pub mod calendar;
@@ -34,6 +35,7 @@ pub fn caldav_router<AP: AuthenticationProvider, C: CalendarStore, S: Subscripti
     store: Arc<C>,
     subscription_store: Arc<S>,
     simplified_home_set: bool,
+    config: Arc<CalDavConfig>,
 ) -> Router {
     Router::new().nest(
         prefix,
@@ -42,9 +44,27 @@ pub fn caldav_router<AP: AuthenticationProvider, C: CalendarStore, S: Subscripti
             sub_store: subscription_store,
             cal_store: store,
             simplified_home_set,
+            config,
         })
         .axum_router()
         .layer(AuthenticationLayer::new(auth_provider))
         .layer(Extension(CalDavPrincipalUri(prefix))),
     )
 }
+
+const fn default_true() -> bool {
+    true
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(deny_unknown_fields, default)]
+pub struct CalDavConfig {
+    #[serde(default = "default_true")]
+    rfc7809: bool,
+}
+
+impl Default for CalDavConfig {
+    fn default() -> Self {
+        Self { rfc7809: true }
+    }
+}
diff --git a/crates/caldav/src/principal/service.rs b/crates/caldav/src/principal/service.rs
index e850649..a6d192b 100644
--- a/crates/caldav/src/principal/service.rs
+++ b/crates/caldav/src/principal/service.rs
@@ -1,7 +1,7 @@
 use crate::calendar::CalendarResourceService;
 use crate::calendar::resource::CalendarResource;
 use crate::principal::PrincipalResource;
-use crate::{CalDavPrincipalUri, Error};
+use crate::{CalDavConfig, CalDavPrincipalUri, Error};
 use async_trait::async_trait;
 use axum::Router;
 use rustical_dav::resource::{AxumMethods, ResourceService};
@@ -20,6 +20,7 @@ pub struct PrincipalResourceService<
     pub(crate) cal_store: Arc<CS>,
     // If true only return the principal as the calendar home set, otherwise also groups
     pub(crate) simplified_home_set: bool,
+    pub(crate) config: Arc<CalDavConfig>,
 }
 
 impl<AP: AuthenticationProvider, S: SubscriptionStore, CS: CalendarStore> Clone
@@ -31,6 +32,7 @@ impl<AP: AuthenticationProvider, S: SubscriptionStore, CS: CalendarStore> Clone
             sub_store: self.sub_store.clone(),
             cal_store: self.cal_store.clone(),
             simplified_home_set: self.simplified_home_set,
+            config: self.config.clone(),
         }
     }
 }
@@ -84,8 +86,12 @@ impl<AP: AuthenticationProvider, S: SubscriptionStore, CS: CalendarStore> Resour
         Router::new()
             .nest(
                 "/{calendar_id}",
-                CalendarResourceService::new(self.cal_store.clone(), self.sub_store.clone())
-                    .axum_router(),
+                CalendarResourceService::new(
+                    self.cal_store.clone(),
+                    self.sub_store.clone(),
+                    self.config.clone(),
+                )
+                .axum_router(),
             )
             .route_service("/", self.axum_service())
     }
diff --git a/crates/caldav/src/principal/tests.rs b/crates/caldav/src/principal/tests.rs
index 2a1954f..9fa0548 100644
--- a/crates/caldav/src/principal/tests.rs
+++ b/crates/caldav/src/principal/tests.rs
@@ -27,6 +27,7 @@ async fn test_principal_resource(
         sub_store: Arc::new(sub_store),
         auth_provider: Arc::new(auth_provider),
         simplified_home_set: false,
+        config: Default::default(),
     };
 
     // We don't have any calendars here
diff --git a/crates/ical/src/address_object.rs b/crates/ical/src/address_object.rs
index 66cb13d..586da51 100644
--- a/crates/ical/src/address_object.rs
+++ b/crates/ical/src/address_object.rs
@@ -17,7 +17,7 @@ use caldata::{
 };
 use chrono::{NaiveDate, Utc};
 use sha2::{Digest, Sha256};
-use std::collections::HashMap;
+use std::collections::BTreeMap;
 use std::str::FromStr;
 
 #[derive(Debug, Clone)]
@@ -134,7 +134,7 @@ impl AddressObject {
                     .into(),
                 ],
                 inner: Some(CalendarInnerDataBuilder::Event(vec![event])),
-                vtimezones: HashMap::default(),
+                vtimezones: BTreeMap::default(),
             }
             .build(None)?
             .into(),
diff --git a/crates/ical/src/calendar_object.rs b/crates/ical/src/calendar_object.rs
index b5e2a1d..78aedb0 100644
--- a/crates/ical/src/calendar_object.rs
+++ b/crates/ical/src/calendar_object.rs
@@ -1,8 +1,11 @@
+use std::sync::OnceLock;
+
 use crate::Error;
 use caldata::{
     IcalObjectParser,
     component::{CalendarInnerData, IcalCalendarObject},
     generator::Emitter,
+    parser::ParserOptions,
 };
 use derive_more::Display;
 use serde::Deserialize;
@@ -65,15 +68,35 @@ impl rustical_xml::ValueDeserialize for CalendarObjectType {
 #[derive(Debug, Clone)]
 pub struct CalendarObject {
     inner: IcalCalendarObject,
-    ics: String,
+    ics: OnceLock<String>,
 }
 
 impl CalendarObject {
+    // This function parses iCalendar data but doesn't cache it
+    // This is meant for iCalendar data coming from outside that might need to be normalised.
+    // For example if timezones are omitted this can be fixed by this function.
+    pub fn import(ics: &str, options: Option<ParserOptions>) -> Result<Self, Error> {
+        let parser =
+            IcalObjectParser::from_slice(ics.as_bytes()).with_options(options.unwrap_or_default());
+        let inner = parser.expect_one()?;
+
+        Ok(Self {
+            inner,
+            ics: OnceLock::new(),
+        })
+    }
+
+    // This function parses iCalendar data and then caches the parsed iCalendar data.
+    // This function is only meant for loading data from a data store where we know the iCalendar
+    // is already in the desired form.
     pub fn from_ics(ics: String) -> Result<Self, Error> {
         let parser = IcalObjectParser::from_slice(ics.as_bytes());
         let inner = parser.expect_one()?;
 
-        Ok(Self { inner, ics })
+        Ok(Self {
+            inner,
+            ics: ics.into(),
+        })
     }
 
     #[must_use]
@@ -96,7 +119,7 @@ impl CalendarObject {
 
     #[must_use]
     pub fn get_ics(&self) -> &str {
-        &self.ics
+        self.ics.get_or_init(|| self.inner.generate())
     }
 
     #[must_use]
@@ -114,7 +137,7 @@ impl From<CalendarObject> for IcalCalendarObject {
 impl From<IcalCalendarObject> for CalendarObject {
     fn from(value: IcalCalendarObject) -> Self {
         Self {
-            ics: value.generate(),
+            ics: value.generate().into(),
             inner: value,
         }
     }
diff --git a/src/app.rs b/src/app.rs
index 4b2f6a1..44691e8 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -9,7 +9,7 @@ use axum_extra::TypedHeader;
 use headers::{HeaderMapExt, UserAgent};
 use http::header::CONNECTION;
 use http::{HeaderValue, StatusCode};
-use rustical_caldav::caldav_router;
+use rustical_caldav::{CalDavConfig, caldav_router};
 use rustical_carddav::carddav_router;
 use rustical_frontend::nextcloud_login::nextcloud_login_router;
 use rustical_frontend::{FrontendConfig, frontend_router};
@@ -45,6 +45,7 @@ pub fn make_app<
     auth_provider: Arc<impl AuthenticationProvider>,
     frontend_config: FrontendConfig,
     oidc_config: Option<OidcConfig>,
+    caldav_config: CalDavConfig,
     nextcloud_login_config: &NextcloudLoginConfig,
     dav_push_enabled: bool,
     session_cookie_samesite_strict: bool,
@@ -54,6 +55,8 @@ pub fn make_app<
     let combined_cal_store =
         Arc::new(CombinedCalendarStore::new(cal_store).with_store(birthday_store));
 
+    let caldav_config = Arc::new(caldav_config);
+
     let mut router = Router::new()
         // endpoint to be used by healthcheck to see if rustical is online
         .route("/ping", axum::routing::get(async || "Pong!"))
@@ -63,6 +66,7 @@ pub fn make_app<
             combined_cal_store.clone(),
             subscription_store.clone(),
             false,
+            caldav_config.clone(),
         ))
         .merge(caldav_router(
             "/caldav-compat",
@@ -70,6 +74,7 @@ pub fn make_app<
             combined_cal_store.clone(),
             subscription_store.clone(),
             true,
+            caldav_config,
         ))
         .route(
             "/.well-known/caldav",
diff --git a/src/commands/mod.rs b/src/commands/mod.rs
index 7614232..072bb8c 100644
--- a/src/commands/mod.rs
+++ b/src/commands/mod.rs
@@ -3,6 +3,7 @@ use crate::config::{
     SqliteDataStoreConfig, TracingConfig,
 };
 use clap::Parser;
+use rustical_caldav::CalDavConfig;
 use rustical_frontend::FrontendConfig;
 
 pub mod health;
@@ -15,6 +16,7 @@ pub struct GenConfigArgs {}
 pub fn cmd_gen_config(_args: GenConfigArgs) -> anyhow::Result<()> {
     let config = Config {
         http: HttpConfig::default(),
+        caldav: CalDavConfig::default(),
         data_store: DataStoreConfig::Sqlite(SqliteDataStoreConfig {
             db_url: "/var/lib/rustical/db.sqlite3".to_owned(),
             run_repairs: true,
diff --git a/src/config.rs b/src/config.rs
index 3a23f66..3e271a6 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -1,3 +1,4 @@
+use rustical_caldav::CalDavConfig;
 use rustical_frontend::FrontendConfig;
 use rustical_oidc::OidcConfig;
 use serde::{Deserialize, Serialize};
@@ -97,4 +98,6 @@ pub struct Config {
     pub dav_push: DavPushConfig,
     #[serde(default)]
     pub nextcloud_login: NextcloudLoginConfig,
+    #[serde(default)]
+    pub caldav: CalDavConfig,
 }
diff --git a/src/integration_tests/mod.rs b/src/integration_tests/mod.rs
index 17c0d1f..18a8514 100644
--- a/src/integration_tests/mod.rs
+++ b/src/integration_tests/mod.rs
@@ -2,6 +2,7 @@ use crate::{app::make_app, config::NextcloudLoginConfig};
 use axum::extract::Request;
 use axum::{body::Body, response::Response};
 use rstest::rstest;
+use rustical_caldav::CalDavConfig;
 use rustical_frontend::FrontendConfig;
 use rustical_store_sqlite::tests::{TestStoreContext, test_store_context};
 use std::sync::Arc;
@@ -26,6 +27,7 @@ pub fn get_app(context: TestStoreContext) -> axum::Router {
             allow_password_login: true,
         },
         None,
+        CalDavConfig::default(),
         &NextcloudLoginConfig { enabled: false },
         false,
         true,
diff --git a/src/main.rs b/src/main.rs
index ae7896d..8743d1a 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -153,6 +153,7 @@ async fn main() -> Result<()> {
                 principal_store.clone(),
                 config.frontend.clone(),
                 config.oidc.clone(),
+                config.caldav,
                 &config.nextcloud_login,
                 config.dav_push.enabled,
                 config.http.session_cookie_samesite_strict,