diff --git a/src/action/common/place_nix_configuration.rs b/src/action/common/place_nix_configuration.rs
index 5509e9c0d..8a86bfe89 100644
--- a/src/action/common/place_nix_configuration.rs
+++ b/src/action/common/place_nix_configuration.rs
@@ -5,6 +5,7 @@ use crate::action::base::{CreateDirectory, CreateOrMergeNixConfig};
 use crate::action::{
     Action, ActionDescription, ActionError, ActionErrorKind, ActionTag, StatefulAction,
 };
+use std::collections::hash_map::Entry;
 
 const NIX_CONF_FOLDER: &str = "/etc/nix";
 const NIX_CONF: &str = "/etc/nix/nix.conf";
@@ -32,10 +33,21 @@ impl PlaceNixConfiguration {
         let settings = nix_config.settings_mut();
 
         settings.insert("build-users-group".to_string(), nix_build_group_name);
-        settings.insert(
-            "experimental-features".to_string(),
-            "nix-command flakes auto-allocate-uids".to_string(),
-        );
+        let experimental_features = ["nix-command", "flakes", "auto-allocate-uids"];
+        match settings.entry("experimental-features".to_string()) {
+            Entry::Occupied(mut slot) => {
+                let slot_mut = slot.get_mut();
+                for experimental_feature in experimental_features {
+                    if !slot_mut.contains(experimental_feature) {
+                        *slot_mut += " ";
+                        *slot_mut += experimental_feature;
+                    }
+                }
+            },
+            Entry::Vacant(slot) => {
+                let _ = slot.insert(experimental_features.join(" ").to_string());
+            },
+        };
         settings.insert("auto-optimise-store".to_string(), "true".to_string());
         settings.insert(
             "bash-prompt-prefix".to_string(),
diff --git a/src/settings.rs b/src/settings.rs
index 6d8ea6802..d41bceec3 100644
--- a/src/settings.rs
+++ b/src/settings.rs
@@ -140,7 +140,7 @@ pub struct CommonSettings {
     pub ssl_cert_file: Option<PathBuf>,
 
     /// Extra configuration lines for `/etc/nix.conf`
-    #[cfg_attr(feature = "cli", clap(long, action = ArgAction::Set, num_args = 0.., value_delimiter = ',', env = "NIX_INSTALLER_EXTRA_CONF", global = true))]
+    #[cfg_attr(feature = "cli", clap(long, action = ArgAction::Append, num_args = 0.., env = "NIX_INSTALLER_EXTRA_CONF", global = true))]
     pub extra_conf: Vec<String>,
 
     /// If `nix-installer` should forcibly recreate files it finds existing