diff --git a/rslib/src/scheduler/answering/mod.rs b/rslib/src/scheduler/answering/mod.rs
index 6ff8c6e2d..bf4808a67 100644
--- a/rslib/src/scheduler/answering/mod.rs
+++ b/rslib/src/scheduler/answering/mod.rs
@@ -488,6 +488,9 @@ impl Collection {
             let params = config.fsrs_params();
             if params.len() >= 19 {
                 params[17] > 0.0 && params[18] > 0.0
+            } else if params.is_empty() {
+                // fallback to true when using default params
+                true
             } else {
                 false
             }