diff --git a/Cargo.lock b/Cargo.lock
index b5a997e..5b8296c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,15 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "aho-corasick"
+version = "0.7.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cc936419f96fa211c1b9166887b38e5e40b19958e5b895be7c1f93adec7071ac"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "anyhow"
 version = "1.0.68"
@@ -37,6 +46,7 @@ dependencies = [
  "impl_cast",
  "paste",
  "pollster",
+ "regex",
  "reqwest",
  "rumqttc",
  "serde",
@@ -784,6 +794,8 @@ version = "1.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e076559ef8e241f2ae3479e36f97bd5741c0330689e217ad51ce2c76808b868a"
 dependencies = [
+ "aho-corasick",
+ "memchr",
  "regex-syntax",
 ]
 
diff --git a/Cargo.toml b/Cargo.toml
index 88c4aaa..21ac022 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -27,6 +27,7 @@ tracing = "0.1.37"
 tracing-subscriber = { version = "0.3.16", features = ["env-filter"] }
 bytes = "1.3.0"
 pollster = "0.2.5"
+regex = "1.7.0"
 
 [profile.release]
 lto=true
diff --git a/config/zeus.dev.toml b/config/zeus.dev.toml
index 58fa33f..223b402 100644
--- a/config/zeus.dev.toml
+++ b/config/zeus.dev.toml
@@ -5,6 +5,10 @@ base_url = "https://login.huizinga.dev/api/oidc"
 host="olympus.lan.huizinga.dev"
 port=8883
 username="mqtt"
+password="${MQTT_PASSWORD}"
+
+[ntfy]
+topic = "${NTFY_TOPIC}"
 
 [presence]
 topic = "automation_dev/presence"
diff --git a/src/config.rs b/src/config.rs
index 36c7180..14ebfed 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -1,6 +1,7 @@
 use std::{fs, error::Error, collections::HashMap, net::{Ipv4Addr, SocketAddr}};
 
-use tracing::{debug, trace};
+use regex::{Regex, Captures};
+use tracing::{debug, trace, warn};
 use rumqttc::AsyncClient;
 use serde::Deserialize;
 
@@ -14,7 +15,6 @@ pub struct Config {
     pub mqtt: MqttConfig,
     #[serde(default)]
     pub fullfillment: FullfillmentConfig,
-    #[serde(default)]
     pub ntfy: NtfyConfig,
     pub presence: MqttDeviceConfig,
     pub light_sensor: LightSensorConfig,
@@ -33,7 +33,7 @@ pub struct MqttConfig {
     pub host: String,
     pub port: u16,
     pub username: String,
-    pub password: Option<String>,
+    pub password: String,
 }
 
 #[derive(Debug, Deserialize)]
@@ -68,19 +68,13 @@ fn default_fullfillment_port() -> u16 {
 pub struct NtfyConfig {
     #[serde(default = "default_ntfy_url")]
     pub url: String,
-    pub topic: Option<String>,
+    pub topic: String,
 }
 
 fn default_ntfy_url() -> String {
     "https://ntfy.sh".into()
 }
 
-impl Default for NtfyConfig {
-    fn default() -> Self {
-        Self { url: default_ntfy_url(), topic: None }
-    }
-}
-
 #[derive(Debug, Deserialize)]
 pub struct LightSensorConfig {
     #[serde(flatten)]
@@ -161,11 +155,23 @@ impl Config {
     pub fn build(filename: &str) -> Result<Self, Box<dyn Error>> {
         debug!("Loading config: {filename}");
         let file = fs::read_to_string(filename)?;
-        let mut config: Self = toml::from_str(&file)?;
 
-        config.mqtt.password = Some(std::env::var("MQTT_PASSWORD").or(config.mqtt.password.ok_or("MQTT password needs to be set in either config [mqtt.password] or the environment [MQTT_PASSWORD]"))?);
-        config.ntfy.topic = Some(std::env::var("NTFY_TOPIC").or(config.ntfy.topic.ok_or("ntfy.sh topic needs to be set in either config [ntfy.url] or the environment [NTFY_TOPIC]!"))?);
+        // Substitute in environment variables
+        let re = Regex::new(r"\$\{(.*)\}").unwrap();
+        let file = re.replace_all(&file, |caps: &Captures| {
+            let key = caps.get(1).unwrap().as_str();
+            debug!("Substituting '{key}' in config");
+            match std::env::var(key) {
+                Ok(value) => value,
+                Err(_) => {
+                    // @TODO Would be nice if we could propagate this error upwards
+                    warn!("Environment variable '{key}' is not set, using empty string as default");
+                    "".to_string()
+                }
+            }
+        });
 
+        let config = toml::from_str(&file)?;
         Ok(config)
     }
 }
diff --git a/src/main.rs b/src/main.rs
index 4118cb8..539c035 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,5 +1,5 @@
 #![feature(async_closure)]
-use std::{time::Duration, sync::{Arc, RwLock}, process, net::SocketAddr};
+use std::{time::Duration, sync::{Arc, RwLock}, process};
 
 use axum::{Router, Json, routing::post, http::StatusCode, extract::FromRef};
 
@@ -45,7 +45,7 @@ async fn main() {
 
     // Configure MQTT
     let mut mqttoptions = MqttOptions::new("rust-test", config.mqtt.host, config.mqtt.port);
-    mqttoptions.set_credentials(config.mqtt.username, config.mqtt.password.unwrap());
+    mqttoptions.set_credentials(config.mqtt.username, config.mqtt.password);
     mqttoptions.set_keep_alive(Duration::from_secs(5));
     mqttoptions.set_transport(Transport::tls_with_default_config());
 
diff --git a/src/ntfy.rs b/src/ntfy.rs
index 88fca77..de2b36f 100644
--- a/src/ntfy.rs
+++ b/src/ntfy.rs
@@ -89,7 +89,7 @@ impl Notification {
 
 impl Ntfy {
     pub fn new(config: NtfyConfig) -> Self {
-        Self { base_url: config.url, topic: config.topic.unwrap() }
+        Self { base_url: config.url, topic: config.topic }
     }
 }