diff --git a/agent/src/agents/twitch.ts b/agent/src/agents/twitch.ts
index a442b4181..db6388b0c 100644
--- a/agent/src/agents/twitch.ts
+++ b/agent/src/agents/twitch.ts
@@ -478,35 +478,48 @@ async function join(
       .orderBy("createdAt", "desc")
       .onSnapshot(async (snapshot) => {
         for (const change of snapshot.docChanges()) {
-          if (change.type == "added") {
-            // verify that the user id matches the channel id.
-            const userId = change.doc.get("userId");
-            if (userId) {
-              const channelId = await getChannelId(userId, "twitch");
-              if (channelId != `twitch:${authProvider.providerId}`) {
-                continue;
-              }
-            }
-            const targetChannel = change.doc.get("targetChannel");
-            const message = change.doc.get("message");
-            if (!targetChannel || !message) {
+          if (change.type != "added") {
+            continue;
+          }
+          // verify that the user id matches the channel id.
+          const userId = change.doc.get("userId");
+          if (userId) {
+            const channelId = await getChannelId(userId, "twitch");
+            if (channelId != `twitch:${authProvider.providerId}`) {
               continue;
             }
-            try {
-              await send.say(targetChannel, message);
-              await change.doc.ref.update({
-                sentAt: admin.firestore.FieldValue.serverTimestamp(),
-              });
-            } catch (e: any) {
-              log.error(
-                { error: e, targetChannel, message },
-                "error sending message"
-              );
-              await change.doc.ref.update({
-                error: e.message,
+          }
+          const targetChannel = change.doc.get("targetChannel");
+          const message = change.doc.get("message");
+          if (!targetChannel || !message) {
+            continue;
+          }
+          try {
+            await admin.firestore().runTransaction(async (transaction) => {
+              const doc = await transaction.get(change.doc.ref);
+              if (doc.get("sentAt")) {
+                return;
+              }
+              transaction.update(change.doc.ref, {
                 sentAt: admin.firestore.FieldValue.serverTimestamp(),
               });
-            }
+            });
+          } catch (error) {
+            // transaction failed, probably because it was already sent.
+            continue;
+          }
+          try {
+            await send.say(targetChannel, message);
+            await change.doc.ref.update({ isComplete: true });
+          } catch (e: any) {
+            log.error(
+              { error: e, targetChannel, message },
+              "error sending message"
+            );
+            await change.doc.ref.update({
+              isComplete: true,
+              error: e.message,
+            });
           }
         }
       });