diff --git a/modules/mesh-delivery-indexer/internal/index/pending.go b/modules/mesh-delivery-indexer/internal/index/pending.go
index 9999039f..08128919 100644
--- a/modules/mesh-delivery-indexer/internal/index/pending.go
+++ b/modules/mesh-delivery-indexer/internal/index/pending.go
@@ -1307,7 +1307,23 @@ func (ix *Indexer) DropPending(ctx context.Context, key, by, why string, abandon
 	}
 	e := entries[at]
 	if !abandon {
-		covered := slices.ContainsFunc(entries[at+1:], func(o PendingEntry) bool { return o.Forge.Repository == e.Forge.Repository })
+		// Covered: a later merge of the same repository, pending or taken in, has this merge's commit as an ancestor (ADR
+		// 0668 §6), asked of the forge (older); a later merge whose history does not hold it covers nothing.
+		covered := false
+		for _, o := range entries[at+1:] {
+			if o.Forge.Repository != e.Forge.Repository {
+				continue
+			}
+			in, err := ix.older(ctx, e.Forge.Repository, e.Forge.Merge, o.Forge.Merge)
+			if err != nil {
+				r.Answer = fmt.Sprintf("%s is not dropped: whether the later pending merge %s covers it is not read: %v", key, o.Key, err)
+				return r
+			}
+			if in {
+				covered = true
+				break
+			}
+		}
 		if !covered {
 			taken, err := ix.takenAlready(ctx, forgemsg.GroupMerge{Repository: e.Forge.Repository, Number: e.Forge.Number, Merge: e.Forge.Merge})
 			if err != nil {
@@ -1317,7 +1333,7 @@ func (ix *Indexer) DropPending(ctx context.Context, key, by, why string, abandon
 			covered = taken
 		}
 		if !covered {
-			r.Answer = fmt.Sprintf("%s is not dropped: no later merge of %s is pending and its taken merge does not cover %s, so its "+
+			r.Answer = fmt.Sprintf("%s is not dropped: no later merge of %s, pending or taken in, has %s as an ancestor, so its "+
 				"changes would never be taken in (ADR 0633 §5); %s reads its message again, or abandon: true drops it all the same",
 				key, e.Forge.Repository, e.Forge.Merge, TakeInPendingTool)
 			return r
diff --git a/modules/mesh-delivery-indexer/internal/index/pending_test.go b/modules/mesh-delivery-indexer/internal/index/pending_test.go
index c0bd87e8..e41d3c03 100644
--- a/modules/mesh-delivery-indexer/internal/index/pending_test.go
+++ b/modules/mesh-delivery-indexer/internal/index/pending_test.go
@@ -711,6 +711,17 @@ func TestTakeIn(t *testing.T) { // 1585/T3-T13 (ADR 0633)
 			answer.Waits[0].Said != takein.TakeInPendingEvent || len(answer.Waits[0].Keys) != 2 {
 			t.Fatalf("indexer_pending = %+v", answer)
 		}
+		// ADR 0668 §6: a later merge covers a pending one only when its commit has the pending merge's as an ancestor.
+		history := "cd"
+		b.ix.Contains = func(_ context.Context, _, commit, in string) (bool, error) {
+			i, j := strings.IndexByte(history, commit[0]), strings.IndexByte(history, in[0])
+			return i >= 0 && j >= 0 && i <= j, nil
+		}
+		history = "dc" // m.3's commit is not in m.2's later history (a history rewritten)
+		if r := b.ix.DropPending(ctx, takein.PendingKey(2), "lead@shanks", "replaced by m.3", false); r.Stored || !strings.Contains(r.Answer, "as an ancestor") {
+			t.Fatalf("a drop a later merge not holding it would cover: %+v", r)
+		}
+		history = "cd"
 		b.said = nil
 		if r := b.ix.DropPending(ctx, takein.PendingKey(2), "lead@shanks", "replaced by m.3", false); !r.Stored {
 			t.Fatalf("drop: %+v", r)