diff --git a/apps/ios/Shared/Views/Chat/Group/GroupMentions.swift b/apps/ios/Shared/Views/Chat/Group/GroupMentions.swift
index cdbed7fe30..2862e1099a 100644
--- a/apps/ios/Shared/Views/Chat/Group/GroupMentions.swift
+++ b/apps/ios/Shared/Views/Chat/Group/GroupMentions.swift
@@ -173,7 +173,7 @@ struct GroupMentionsView: View {
         let usedMentions: Set<String> = Set(parsedMsg.compactMap { ft in
             if case let .mention(name) = ft.format { name } else { nil }
         })
-        if usedMentions.count < composeState.mentions.count  {
+        if composeState.mentions.contains(where: { !usedMentions.contains($0.key) }) {
             composeState = composeState.copy(mentions: composeState.mentions.filter({ usedMentions.contains($0.key) }))
         }
     }
diff --git a/apps/multiplatform/common/src/commonMain/kotlin/chat/simplex/common/views/chat/group/GroupMentions.kt b/apps/multiplatform/common/src/commonMain/kotlin/chat/simplex/common/views/chat/group/GroupMentions.kt
index aa737a02d3..dbb9ace70a 100644
--- a/apps/multiplatform/common/src/commonMain/kotlin/chat/simplex/common/views/chat/group/GroupMentions.kt
+++ b/apps/multiplatform/common/src/commonMain/kotlin/chat/simplex/common/views/chat/group/GroupMentions.kt
@@ -318,7 +318,7 @@ private fun removeUnusedMentions(composeState: MutableState<ComposeState>, parse
     }
   }.toSet()
 
-  if (usedMentions.size < composeState.value.mentions.size) {
+  if (composeState.value.mentions.keys.any { it !in usedMentions }) {
     composeState.value = composeState.value.copy(
       mentions = composeState.value.mentions.filterKeys { it in usedMentions }
     )
diff --git a/plans/2026-05-26-fix-invalid-mention-on-edit.md b/plans/2026-05-26-fix-invalid-mention-on-edit.md
new file mode 100644
index 0000000000..04e7b1e50b
--- /dev/null
+++ b/plans/2026-05-26-fix-invalid-mention-on-edit.md
@@ -0,0 +1,49 @@
+# Fix: "error store invalidMention" when an inserted @mention is edited in place
+
+## Symptom
+
+Rare "Error sending message: error store invalidMention" when sending a group
+message that contains an @mention.
+
+## Root cause
+
+`removeUnusedMentions` in both `GroupMentions.kt` and `GroupMentions.swift`
+prunes the compose-state `mentions` map only when the number of parsed
+`@name` tokens is **strictly less** than the number of entries in the map:
+
+```kotlin
+if (usedMentions.size < composeState.value.mentions.size) { ... }
+```
+
+When the user picks a member from the picker, the client inserts `@Name` into
+the message text and records `mentions[Name] = memberId`. If the user then
+**edits the inserted token in place** (e.g. fixes a typo, deletes one
+character) without re-picking from the picker, the parser sees one mention
+with the new name while the map still contains the old name. Both have size 1,
+so the guard does not fire and the stale entry is sent to the core.
+
+The core's `getCIMentions` (`Internal.hs:267-271`) requires every key in the
+client-supplied mentions map to also appear as a parsed `@name` token in the
+message text, and throws `SEInvalidMention` otherwise.
+
+## Fix
+
+Prune whenever any map key is missing from the set of parsed mention names,
+regardless of count. After pruning, the edited `@name` token becomes a plain
+formatted mention with no member binding — exactly the desired behaviour for a
+token the user has modified away from the originally picked member.
+
+- `apps/multiplatform/.../GroupMentions.kt:321`
+- `apps/ios/.../GroupMentions.swift:176`
+
+Both clients had the identical bug; both are patched.
+
+## Manual reproduction
+
+1. In a group, type `@` and pick a member from the picker. Text becomes
+   `@Name ` and the mentions map gets `{Name → memberId}`.
+2. Place the cursor inside the inserted name and add or delete one character
+   (`@Nam`, `@Names`, etc.) — do not use the picker.
+3. Tap send. Before the fix: send fails with `error store invalidMention`.
+   After the fix: message is sent, the modified token appears as a plain
+   formatted `@` token with no member link.