diff --git a/src/model.rs b/src/model.rs
index ab5b2f9..83c38bd 100644
--- a/src/model.rs
+++ b/src/model.rs
@@ -250,6 +250,8 @@ pub(crate) fn check_and_fill_parameters(parameters: &Parameters) -> Result<Vec<f
         0 => DEFAULT_PARAMETERS.to_vec(),
         17 => {
             let mut parameters = parameters.to_vec();
+            parameters[4] = parameters[5].mul_add(2.0, parameters[4]);
+            parameters[5] = parameters[5].mul_add(3.0, 1.0).ln() / 3.0;
             parameters.extend_from_slice(&[0.0, 0.0]);
             parameters
         }
@@ -274,6 +276,22 @@ mod tests {
         assert_eq!(model.w.val().to_data(), Data::from(DEFAULT_PARAMETERS))
     }
 
+    #[test]
+    fn convert_parameters() {
+        let fsrs4dot5_param = vec![
+            0.4, 0.6, 2.4, 5.8, 4.93, 0.94, 0.86, 0.01, 1.49, 0.14, 0.94, 2.18, 0.05, 0.34, 1.26,
+            0.29, 2.61,
+        ];
+        let fsrs5_param = check_and_fill_parameters(&fsrs4dot5_param).unwrap();
+        assert_eq!(
+            fsrs5_param,
+            vec![
+                0.4, 0.6, 2.4, 5.8, 6.81, 0.44675013, 0.86, 0.01, 1.49, 0.14, 0.94, 2.18, 0.05,
+                0.34, 1.26, 0.29, 2.61, 0.0, 0.0,
+            ]
+        )
+    }
+
     #[test]
     fn power_forgetting_curve() {
         let device = NdArrayDevice::Cpu;
diff --git a/src/optimal_retention.rs b/src/optimal_retention.rs
index e04737a..f824a21 100644
--- a/src/optimal_retention.rs
+++ b/src/optimal_retention.rs
@@ -1144,9 +1144,9 @@ mod tests {
             learn_limit,
             ..Default::default()
         };
-        let optimal_retention = fsrs
-            .optimal_retention(&config, &DEFAULT_PARAMETERS[..17], |_v| true)
-            .unwrap();
+        let mut param = DEFAULT_PARAMETERS[..17].to_vec();
+        param.extend_from_slice(&[0.0, 0.0]);
+        let optimal_retention = fsrs.optimal_retention(&config, &param, |_v| true).unwrap();
         assert_eq!(optimal_retention, 0.85450846);
         Ok(())
     }