diff --git a/proposer/op/proposer/prove.go b/proposer/op/proposer/prove.go
index 520c1bfd..85f4f29a 100644
--- a/proposer/op/proposer/prove.go
+++ b/proposer/op/proposer/prove.go
@@ -240,6 +240,10 @@ type ProofResponse struct {
 
 // Request a span proof for the range [l2Start, l2End].
 func (l *L2OutputSubmitter) RequestSpanProof(l2Start, l2End uint64) (string, error) {
+	if l2Start >= l2End {
+		return "", fmt.Errorf("l2Start must be greater than l2End")
+	}
+
 	l.Log.Info("requesting span proof", "start", l2Start, "end", l2End)
 	requestBody := SpanProofRequest{
 		Start: l2Start,