diff --git a/src/client/client.ts b/src/client/client.ts
index 6248a44..3ab3964 100644
--- a/src/client/client.ts
+++ b/src/client/client.ts
@@ -83,6 +83,13 @@ export class ScramjetClient {
 	meta: URLMeta;
 
 	constructor(public global: typeof globalThis) {
+		if (SCRAMJETCLIENT in global) {
+			console.error(
+				"attempted to initialize a scramjet client, but one is already loaded - this is very bad"
+			);
+			throw new Error();
+		}
+
 		this.serviceWorker = this.global.navigator.serviceWorker;
 
 		if (iswindow) {