diff --git a/consensus/validation.go b/consensus/validation.go
index 8519e963..f757721a 100644
--- a/consensus/validation.go
+++ b/consensus/validation.go
@@ -11,9 +11,16 @@ import (
 	"go.sia.tech/core/types"
 )
 
+var (
+	// ErrFutureBlock is returned when a block's timestamp is too far in the future.
+	ErrFutureBlock = errors.New("block's timestamp is too far in the future")
+)
+
 func validateHeader(s State, parentID types.BlockID, timestamp time.Time, nonce uint64, id types.BlockID) error {
 	if parentID != s.Index.ID {
 		return errors.New("wrong parent ID")
+	} else if timestamp.After(s.MaxFutureTimestamp(time.Now())) {
+		return ErrFutureBlock
 	} else if timestamp.Before(s.medianTimestamp()) {
 		return errors.New("timestamp is too far in the past")
 	} else if nonce%s.NonceFactor() != 0 {