diff --git a/value_provider.go b/value_provider.go
index ddb894a..90aec9d 100644
--- a/value_provider.go
+++ b/value_provider.go
@@ -19,7 +19,7 @@ type LastValueProvider interface {
 
 // BoundedLastValueProvider is a special type of value provider that can return it's (potentially computed) bounded last value.
 type BoundedLastValueProvider interface {
-	GetBoundedLastValue(index int) (x, y1, y2 float64)
+	GetBoundedLastValue() (x, y1, y2 float64)
 }
 
 // FullValueProvider is an interface that combines `ValueProvider` and `LastValueProvider`