diff --git a/Cargo.lock b/Cargo.lock
index d29569d..5cb9dd8 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -726,7 +726,7 @@ checksum = "aa9a19cbb55df58761df49b23516a86d432839add4af60fc256da840f66ed35b"
 
 [[package]]
 name = "fsrs"
-version = "1.1.4"
+version = "1.3.3"
 dependencies = [
  "burn",
  "chrono",
@@ -735,6 +735,7 @@ dependencies = [
  "log",
  "ndarray",
  "ndarray-rand",
+ "priority-queue",
  "rand",
  "rayon",
  "serde",
@@ -1526,6 +1527,17 @@ version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e8cf8e6a8aa66ce33f63993ffc4ea4271eb5b0530a9002db8455ea6050c77bfa"
 
+[[package]]
+name = "priority-queue"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "714c75db297bc88a63783ffc6ab9f830698a6705aa0201416931759ef4c8183d"
+dependencies = [
+ "autocfg",
+ "equivalent",
+ "indexmap",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.81"
diff --git a/fsrs-rs b/fsrs-rs
index ed628b0..8ef7197 160000
--- a/fsrs-rs
+++ b/fsrs-rs
@@ -1 +1 @@
-Subproject commit ed628b09c5889e870e70c01f89ac1526325583d8
+Subproject commit 8ef7197bec29470cf4ba612e8383f72eb7f4cfb6
diff --git a/sandbox/tests/prod.spec.ts b/sandbox/tests/prod.spec.ts
index e8e1b13..9502ecb 100644
--- a/sandbox/tests/prod.spec.ts
+++ b/sandbox/tests/prod.spec.ts
@@ -1,4 +1,4 @@
-import { test, expect, Page } from '@playwright/test'
+import { test, expect } from '@playwright/test'
 import { goHome } from './util'
 
 test('check memory state', async ({ page }) => {
@@ -22,13 +22,16 @@ test('check memory state', async ({ page }) => {
 test('check next interval', async ({ page }) => {
 	await goHome(page)
 	await page.getByRole('button', { name: 'Calculate Next Interval' }).click()
-	await expect(page.locator('#nextIntervalResponse')).toHaveText('2')
+	await expect(page.locator('#nextIntervalResponse')).toContainText('.') // ensures that text has updated, so the more specific assertion `.toEqual(2)` can run
+	const nextInterval = await page.locator('#nextIntervalResponse').textContent()
+	const rounded = Math.round(parseFloat(nextInterval))
+	expect(rounded).toEqual(2)
 })
 
 test('check progress and parameters', async ({ page }) => {
 	await goHome(page)
 	await page.getByRole('button', { name: 'Train with example file' }).click()
-	let progress = await page.locator('#progressNumbers').innerText()
+	const progress = await page.locator('#progressNumbers').innerText()
 	expect(progress).toEqual('0/0')
 	await expect
 		.poll(
diff --git a/src/lib.rs b/src/lib.rs
index 0e6d659..7600c71 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -131,7 +131,7 @@ impl FSRSwasm {
         stability: Option<f32>,
         desired_retention: f32,
         rating: u32,
-    ) -> u32 {
+    ) -> f32 {
         self.model
             .next_interval(stability, desired_retention, rating)
     }