diff --git a/manager/src/lib/provisioning.ts b/manager/src/lib/provisioning.ts
index 90c3005..2337d06 100644
--- a/manager/src/lib/provisioning.ts
+++ b/manager/src/lib/provisioning.ts
@@ -188,7 +188,20 @@ export async function updateBusiness(input: UpdateBusinessInput): Promise<Update
   const dir = stackDir(slug);
   const envPath = path.join(dir, ".env");
   const currentEnv = await readEnvFile(envPath);
-  const currentDomain = currentEnv ? readEnvValue(currentEnv, "DOMAIN") : null;
+  if (currentEnv === null) {
+    // stackExists() above only confirms compose.yaml is there — a stack
+    // can have that without ever having been through real provisioning
+    // (e.g. a hand-written example stack that was never actually started
+    // with a real database). Editing one would otherwise silently write
+    // a stub .env containing only the 4 keys below, missing
+    // DATABASE_HOST/NAME/USER/PASSWORD, AUTH_SECRET, etc. entirely —
+    // this happened for real once, see the fix commit for this line.
+    throw new Error(
+      `"${slug}" has no existing configuration to edit — it was never fully provisioned with a database. ` +
+        "Remove its stack directory and use Add Business instead, or complete its setup by hand first (see stacks/infra/compose.yaml's header).",
+    );
+  }
+  const currentDomain = readEnvValue(currentEnv, "DOMAIN");
   const domainChanged = currentDomain !== domain;
 
   // Only these four keys are ever touched — everything else in the file