diff --git a/ofborg/src/bin/builder.rs b/ofborg/src/bin/builder.rs
index b61bb16..f6a0e4d 100644
--- a/ofborg/src/bin/builder.rs
+++ b/ofborg/src/bin/builder.rs
@@ -29,21 +29,15 @@ fn main() -> Result<(), Box<dyn Error>> {
     };
 
     let conn = easylapin::from_config(&cfg.rabbitmq)?;
-    let handle = self::create_handle(&conn, &cfg, None)?;
+    let mut handles = Vec::new();
 
-    if let Some(ref additional_build_systems) = cfg.nix.additional_build_systems {
-        let mut handles = vec![handle];
-
-        for system in additional_build_systems {
-            let handle_ext = self::create_handle(&conn, &cfg, Some(system.to_string()))?;
-            handles.push(handle_ext);
-        }
-
-        task::block_on(future::join_all(handles));
-    } else {
-        task::block_on(handle);
+    for system in &cfg.nix.system {
+        let handle_ext = self::create_handle(&conn, &cfg, system.to_string())?;
+        handles.push(handle_ext);
     }
 
+    task::block_on(future::join_all(handles));
+
     drop(conn); // Close connection.
     info!("Closed the session... EOF");
     Ok(())
@@ -52,17 +46,12 @@ fn main() -> Result<(), Box<dyn Error>> {
 fn create_handle(
     conn: &lapin::Connection,
     cfg: &config::Config,
-    system_override: Option<String>,
+    system: String,
 ) -> Result<JoinHandle<()>, Box<dyn Error>> {
     let mut chan = task::block_on(conn.create_channel())?;
 
     let cloner = checkout::cached_cloner(Path::new(&cfg.checkout.root));
-    let nix = if let Some(system) = system_override {
-        cfg.nix().with_system(String::from(system))
-    } else {
-        cfg.nix()
-    };
-    let system = nix.system.clone();
+    let nix = cfg.nix().with_system(system.clone());
 
     chan.declare_exchange(easyamqp::ExchangeConfig {
         exchange: "build-jobs".to_owned(),
diff --git a/ofborg/src/config.rs b/ofborg/src/config.rs
index 7e93ef2..8fd791e 100644
--- a/ofborg/src/config.rs
+++ b/ofborg/src/config.rs
@@ -2,14 +2,17 @@ use crate::acl;
 use crate::nix::Nix;
 
 use std::collections::HashMap;
+use std::fmt;
 use std::fs::File;
 use std::io::Read;
+use std::marker::PhantomData;
 use std::path::{Path, PathBuf};
 
 use hubcaps::{Credentials, Github, InstallationTokenGenerator, JWTCredentials};
 use hyper::net::HttpsConnector;
 use hyper::Client;
 use hyper_native_tls::NativeTlsClient;
+use serde::de::{self, Deserialize, Deserializer};
 use tracing::{debug, error, info, warn};
 
 #[derive(Serialize, Deserialize, Debug)]
@@ -40,8 +43,8 @@ pub struct RabbitMqConfig {
 
 #[derive(Serialize, Deserialize, Debug)]
 pub struct NixConfig {
-    pub system: String,
-    pub additional_build_systems: Option<Vec<String>>,
+    #[serde(deserialize_with = "deserialize_one_or_many")]
+    pub system: Vec<String>,
     pub remote: String,
     pub build_timeout_seconds: u16,
     pub initial_heap_size: Option<String>,
@@ -88,7 +91,7 @@ pub struct CheckoutConfig {
 
 impl Config {
     pub fn whoami(&self) -> String {
-        format!("{}-{}", self.runner.identity, self.nix.system)
+        format!("{}-{}", self.runner.identity, self.nix.system.join(","))
     }
 
     pub fn acl(&self) -> acl::Acl {
@@ -136,7 +139,11 @@ impl Config {
         }
 
         Nix::new(
-            self.nix.system.clone(),
+            self.nix
+                .system
+                .first()
+                .expect("expected at least one system")
+                .clone(),
             self.nix.remote.clone(),
             self.nix.build_timeout_seconds,
             self.nix.initial_heap_size.clone(),
@@ -224,3 +231,35 @@ impl GithubAppVendingMachine {
         }))
     }
 }
+
+// Copied from https://stackoverflow.com/a/43627388
+fn deserialize_one_or_many<'de, D>(deserializer: D) -> Result<Vec<String>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    struct StringOrVec(PhantomData<Vec<String>>);
+
+    impl<'de> de::Visitor<'de> for StringOrVec {
+        type Value = Vec<String>;
+
+        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            formatter.write_str("string or list of strings")
+        }
+
+        fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
+        where
+            E: de::Error,
+        {
+            Ok(vec![value.to_owned()])
+        }
+
+        fn visit_seq<S>(self, visitor: S) -> Result<Self::Value, S::Error>
+        where
+            S: de::SeqAccess<'de>,
+        {
+            Deserialize::deserialize(de::value::SeqAccessDeserializer::new(visitor))
+        }
+    }
+
+    deserializer.deserialize_any(StringOrVec(PhantomData))
+}