diff --git a/magic-nix-cache/src/env.rs b/magic-nix-cache/src/env.rs
index 464221c..edc6453 100644
--- a/magic-nix-cache/src/env.rs
+++ b/magic-nix-cache/src/env.rs
@@ -1,6 +1,9 @@
-use crate::error::Error;
-use std::env;
+use std::{
+    env,
+    fmt::{self, Display},
+};
 
+#[derive(Clone)]
 pub enum Environment {
     GitHubActions,
     GitLabCI,
@@ -17,30 +20,34 @@ impl Environment {
     }
 }
 
-impl ToString for Environment {
-    fn to_string(&self) -> String {
+impl Display for Environment {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         use Environment::*;
 
-        String::from(match self {
-            GitHubActions => "GitHub Actions",
-            GitLabCI => "GitLab CI",
-            _ => "an unspecified environment",
-        })
+        write!(
+            f,
+            "{}",
+            match self {
+                GitHubActions => "GitHub Actions",
+                GitLabCI => "GitLab CI",
+                Other => "an unspecified environment",
+            }
+        )
     }
 }
 
 pub fn determine_environment() -> Environment {
     if env_var_is_true("GITHUB_ACTIONS") {
-        Environment::GitHubActions
+        return Environment::GitHubActions;
     }
 
     if env_var_is_true("CI") && env_var_is_true("GITLAB_CI") {
-        Environment::GitLabCI
+        return Environment::GitLabCI;
     }
 
     Environment::Other
 }
 
 fn env_var_is_true(e: &str) -> bool {
-    env::var(e).unwrap_or(String::from("")) == String::from("true")
+    &env::var(e).unwrap_or(String::from("")) == "true"
 }
diff --git a/magic-nix-cache/src/error.rs b/magic-nix-cache/src/error.rs
index ae479e1..ec1b8d3 100644
--- a/magic-nix-cache/src/error.rs
+++ b/magic-nix-cache/src/error.rs
@@ -19,9 +19,6 @@ pub enum Error {
     #[error("Bad Request")]
     BadRequest,
 
-    #[error("Current environment couldn't be determinate")]
-    UnknownEnv,
-
     #[error("I/O error: {0}")]
     Io(#[from] std::io::Error),
 
diff --git a/magic-nix-cache/src/main.rs b/magic-nix-cache/src/main.rs
index cd90c12..b0024d6 100644
--- a/magic-nix-cache/src/main.rs
+++ b/magic-nix-cache/src/main.rs
@@ -33,10 +33,10 @@ use anyhow::{anyhow, Context, Result};
 use axum::{extract::Extension, routing::get, Router};
 use clap::Parser;
 use env::Environment;
+use error::Error;
 use tempfile::NamedTempFile;
 use tokio::process::Command;
 use tokio::sync::{oneshot, Mutex, RwLock};
-use tracing_subscriber::field::debug;
 use tracing_subscriber::filter::EnvFilter;
 
 use gha_cache::Credentials;
@@ -125,6 +125,12 @@ impl Args {
             )));
         }
 
+        if environment.is_gitlab_ci() && !self.use_flakehub {
+            return Err(Error::Config(String::from(
+                "you must set --use-flakehub in GitLab CI",
+            )));
+        }
+
         Ok(())
     }
 }
@@ -158,8 +164,8 @@ async fn main_cli() -> Result<()> {
 
     let args = Args::parse();
     let environment = determine_environment();
-    tracing::debug!("Running in {environment}");
-    args.validate(environment)?;
+    tracing::debug!("Running in {}", environment.to_string());
+    args.validate(environment.clone())?;
 
     let metrics = Arc::new(telemetry::TelemetryReport::new());
 
@@ -187,6 +193,7 @@ async fn main_cli() -> Result<()> {
         let flakehub_flake_name = args.flakehub_flake_name;
 
         match flakehub::init_cache(
+            environment,
             &args
                 .flakehub_api_server
                 .ok_or_else(|| anyhow!("--flakehub-api-server is required"))?,