diff --git a/.dev.vars b/.dev.vars
index 5d6d599..27bbe4e 100644
--- a/.dev.vars
+++ b/.dev.vars
@@ -1,2 +1 @@
 API_TOKEN=amogus
-R2_PUBLIC_URL=R2_PLACERHOLDER_PUBLIC_URL
\ No newline at end of file
diff --git a/src/select-zls-version.ts b/src/select-zls-version.ts
index 825af48..ffc50a4 100644
--- a/src/select-zls-version.ts
+++ b/src/select-zls-version.ts
@@ -76,6 +76,12 @@ export async function handleSelectZLSVersion(
     });
   }
 
+  if (typeof env.R2_PUBLIC_URL !== "string" || !env.R2_PUBLIC_URL) {
+    return new Response(null, {
+      status: 500, // Internal Server Error
+    });
+  }
+
   const url = new URL(request.url);
   const zigVersionString = url.searchParams.get("zig_version");
 
diff --git a/wrangler.toml b/wrangler.toml
index c1af31e..ca2805a 100644
--- a/wrangler.toml
+++ b/wrangler.toml
@@ -6,8 +6,8 @@ compatibility_flags = ["nodejs_compat"]
 # Variable bindings. These are arbitrary, plaintext strings (similar to environment variables)
 # Note: Use secrets to store sensitive data.
 # Docs: https://developers.cloudflare.com/workers/wrangler/configuration/#environment-variables
-# [vars]
-# MY_VARIABLE = "production_value"
+[vars]
+R2_PUBLIC_URL="https://builds.zigtools.org"
 
 # Bind a D1 database. D1 is Cloudflare’s native serverless SQL database.
 # Docs: https://developers.cloudflare.com/workers/wrangler/configuration/#d1-databases