diff --git a/functions/api/events-team/events/[id]/complete.ts b/functions/api/events-team/events/[id]/complete.ts
index c2517a8..ce12d2c 100644
--- a/functions/api/events-team/events/[id]/complete.ts
+++ b/functions/api/events-team/events/[id]/complete.ts
@@ -5,6 +5,18 @@ export async function onRequestPost(context: RequestContext) {
   const { event } = context.data;
 
   try {
+    const completionTimeRow = await D1.prepare(
+      "SELECT performed_at FROM events WHERE id = ?;",
+    )
+      .bind(event.id)
+      .first();
+
+    if (typeof completionTimeRow?.performed_at !== "number")
+      return jsonError(
+        "The event is already marked as complete or forgotten",
+        400,
+      );
+
     await D1.batch([
       D1.prepare("UPDATE events SET performed_at = ? WHERE id = ?;").bind(
         Date.now(),
diff --git a/functions/api/events-team/events/[id]/forgotten.ts b/functions/api/events-team/events/[id]/forgotten.ts
index 11f83e4..935fa81 100644
--- a/functions/api/events-team/events/[id]/forgotten.ts
+++ b/functions/api/events-team/events/[id]/forgotten.ts
@@ -5,6 +5,15 @@ export async function onRequestPost(context: RequestContext) {
   const { event } = context.data;
 
   try {
+    const row = await D1.prepare(
+      "SELECT performed_at FROM events WHERE id = ?;",
+    )
+      .bind(event.id)
+      .first();
+
+    if (typeof row?.performed_at !== "number")
+      return jsonError("Event already marked as completed or forgotten", 400);
+
     await D1.batch([
       D1.prepare("UPDATE events SET performed_at = 0 WHERE id = ?;").bind(
         event.id,