diff --git a/chain/messagepool/selection.go b/chain/messagepool/selection.go
index d510cf950..e42cc7812 100644
--- a/chain/messagepool/selection.go
+++ b/chain/messagepool/selection.go
@@ -47,6 +47,16 @@ func (mp *MessagePool) SelectMessages(ctx context.Context, ts *types.TipSet, tq
 	mp.lk.Lock()
 	defer mp.lk.Unlock()
 
+	// See if we need to prune before selection; excessive buildup can lead to slow selection,
+	// so prune if we have too many messages (ignoring the cooldown).
+	mpCfg := mp.getConfig()
+	if mp.currentSize > mpCfg.SizeLimitHigh {
+		log.Infof("too many messages; pruning before selection")
+		if err := mp.pruneMessages(ctx, ts); err != nil {
+			log.Warnf("error pruning excess messages: %s", err)
+		}
+	}
+
 	// if the ticket quality is high enough that the first block has higher probability
 	// than any other block, then we don't bother with optimal selection because the
 	// first block will always have higher effective performance