diff --git a/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/AccountConcordActions.kt b/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/AccountConcordActions.kt
index a52dbc5e38..153877b2da 100644
--- a/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/AccountConcordActions.kt
+++ b/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/AccountConcordActions.kt
@@ -1169,7 +1169,14 @@ class AccountConcordActions(
      */
     suspend fun acceptConcordDirectInvite(wrapId: HexKey): ConcordInviteResult {
         if (!account.isWriteable()) return ConcordInviteResult.InvalidLink
-        acceptingConcordDirectInvites.update { it + wrapId }
+        // Check-and-set in one step: two accepts of one invite would run two joins and announce two
+        // Guestbook JOINs.
+        var claimed = false
+        acceptingConcordDirectInvites.update { current ->
+            claimed = wrapId !in current
+            if (claimed) current + wrapId else current
+        }
+        if (!claimed) return ConcordInviteResult.InProgress
         try {
             return acceptConcordDirectInviteNow(wrapId)
         } finally {
diff --git a/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/ConcordInviteResult.kt b/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/ConcordInviteResult.kt
index bb33934c49..b0580cc23b 100644
--- a/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/ConcordInviteResult.kt
+++ b/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/ConcordInviteResult.kt
@@ -76,4 +76,10 @@ sealed interface ConcordInviteResult {
      * missing (CORD-02 §8). Nothing was announced. Retrying can help once the List loads.
      */
     data object NotSaved : ConcordInviteResult
+
+    /**
+     * This invite is already being accepted (a second tap, or the hub and Notifications at once).
+     * Nothing was done; the accept already running reports the outcome.
+     */
+    data object InProgress : ConcordInviteResult
 }
diff --git a/commonsUI/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/screen/loggedIn/chats/publicChannels/concord/ConcordDirectInvites.kt b/commonsUI/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/screen/loggedIn/chats/publicChannels/concord/ConcordDirectInvites.kt
index 48ad973e20..5d54539918 100644
--- a/commonsUI/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/screen/loggedIn/chats/publicChannels/concord/ConcordDirectInvites.kt
+++ b/commonsUI/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/screen/loggedIn/chats/publicChannels/concord/ConcordDirectInvites.kt
@@ -334,6 +334,8 @@ fun ConcordDirectInviteCard(
                         try {
                             when (val result = accountViewModel.account.concord.acceptConcordDirectInvite(invite.wrapId)) {
                                 is ConcordInviteResult.Joined -> nav.nav(Route.ConcordServer(result.communityId))
+                                // The accept already running reports; this tap did nothing.
+                                is ConcordInviteResult.InProgress -> Unit
                                 is ConcordInviteResult.Expired -> accountViewModel.toastManager.toast(Res.string.concord_direct_invites_title, Res.string.concord_invite_failed_expired)
                                 is ConcordInviteResult.Banned -> accountViewModel.toastManager.toast(Res.string.concord_direct_invites_title, Res.string.concord_invite_failed_banned)
                                 is ConcordInviteResult.InvalidLink -> accountViewModel.toastManager.toast(Res.string.concord_direct_invites_title, Res.string.concord_invite_failed_invalid)
diff --git a/commonsUI/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/screen/loggedIn/chats/publicChannels/concord/ConcordInviteScreen.kt b/commonsUI/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/screen/loggedIn/chats/publicChannels/concord/ConcordInviteScreen.kt
index 7086c9ef1d..7a402b798f 100644
--- a/commonsUI/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/screen/loggedIn/chats/publicChannels/concord/ConcordInviteScreen.kt
+++ b/commonsUI/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/screen/loggedIn/chats/publicChannels/concord/ConcordInviteScreen.kt
@@ -147,6 +147,9 @@ fun ConcordInviteScreen(
                         RedeemState.Failed(Res.string.concord_invite_failed, canRetry = true)
                     is ConcordInviteResult.NotSaved ->
                         RedeemState.Failed(Res.string.concord_invite_failed_not_saved, canRetry = true)
+                    // Only a Direct Invite accept reports this; a link redeem never does.
+                    is ConcordInviteResult.InProgress ->
+                        RedeemState.Failed(Res.string.concord_invite_failed, canRetry = true)
                 }
         }
     }