diff --git a/crates/augurs-forecaster/src/power_transforms.rs b/crates/augurs-forecaster/src/power_transforms.rs
index 1642378..adf7f14 100644
--- a/crates/augurs-forecaster/src/power_transforms.rs
+++ b/crates/augurs-forecaster/src/power_transforms.rs
@@ -35,7 +35,7 @@ impl CostFunction for BoxCoxProblem<'_> {
 }
 
 /// Optimize the lambda parameter for the Box-Cox transformation
-pub fn optimize_lambda(data: &[f64]) -> f64 {
+pub (crate) fn optimize_lambda(data: &[f64]) -> f64 {
     let cost = BoxCoxProblem { data: data };
     let init_param = 0.5;
     let solver = BrentOpt::new(-2.0, 2.0);