diff --git a/internal/events/block_confirmations.go b/internal/events/block_confirmations.go
index 1c78b1a..774a1a3 100644
--- a/internal/events/block_confirmations.go
+++ b/internal/events/block_confirmations.go
@@ -202,7 +202,7 @@ func (bcm *blockConfirmationManager) pollBlockFilter() ([]*ethbinding.Hash, erro
 	defer cancel()
 	var blockHashes []*ethbinding.Hash
 	if err := bcm.rpc.CallContext(ctx, &blockHashes, "eth_getFilterChanges", bcm.filterID); err != nil {
-		if strings.Contains(err.Error(), "filter not found") {
+		if strings.Contains(strings.ToLower(err.Error()), "filter not found") {
 			bcm.filterStale = true
 		}
 		return nil, err
diff --git a/internal/events/subscription.go b/internal/events/subscription.go
index 47dbedf..1f5e0ef 100644
--- a/internal/events/subscription.go
+++ b/internal/events/subscription.go
@@ -364,7 +364,7 @@ func (s *subscription) processNewEvents(ctx context.Context) error {
 		s.info.Synchronized = true
 	}
 	if err := s.rpc.CallContext(ctx, &logs, rpcMethod, s.filterID); err != nil {
-		if strings.Contains(err.Error(), "filter not found") {
+		if strings.Contains(strings.ToLower(err.Error()), "filter not found") {
 			s.markFilterStale(ctx, true)
 		}
 		return err