1 files changed, 6 insertions, 0 deletions
diff --git a/internal/casino/plinko.go b/internal/casino/plinko.go
index 867978a..bcfae83 100644
--- a/internal/casino/plinko.go
+++ b/internal/casino/plinko.go
@@ -29,6 +29,12 @@ func validatePlinko(c TableConfig) error {
 	if math.IsNaN(r) || math.IsInf(r, 0) || r < 31 || r > 100 {
 		return fmt.Errorf("plinko rtp must be between 31 and 100 percent")
 	}
+	// The one-decimal paytable rounding can push the realized expert return
+	// above 100%. Reject any target whose expert paytable pays more than it
+	// takes, so the house never runs a losing plinko board.
+	if ret := plinkoReturn(3, r); ret > 1.0 {
+		return fmt.Errorf("plinko rtp %.1f makes the expert paytable return %.3f%%; lower it", r, 100*ret)
+	}
 	if c.MaxPlayers > 1 {
 		return fmt.Errorf("plinko has one seat")
 	}