diff --git a/app/src/main/java/io/github/mattpvaughn/chronicle/application/ChronicleBillingManager.kt b/app/src/main/java/io/github/mattpvaughn/chronicle/application/ChronicleBillingManager.kt
index 4d7935a..dd584cd 100644
--- a/app/src/main/java/io/github/mattpvaughn/chronicle/application/ChronicleBillingManager.kt
+++ b/app/src/main/java/io/github/mattpvaughn/chronicle/application/ChronicleBillingManager.kt
@@ -46,7 +46,8 @@ class ChronicleBillingManager @Inject constructor(
                 Timber.i("Retrieved purchase list but it was empty or null: ${purchase.purchasesList}")
                 return
             }
-            val premiumSku = purchase.purchasesList!!.find { record -> record.sku == PREMIUM_IAP_SKU }
+            val premiumSku =
+                purchase.purchasesList!!.find { record -> PREMIUM_IAP_SKU in record.skus }
             if (premiumSku != null && premiumSku.purchaseState == PURCHASED) {
                 Timber.i("Found premium SKU in user's history: $premiumSku")
                 prefsRepo.premiumPurchaseToken = premiumSku.purchaseToken
diff --git a/build.gradle b/build.gradle
index b5f688b..6e2ba31 100644
--- a/build.gradle
+++ b/build.gradle
@@ -32,7 +32,7 @@ buildscript {
         localBroadcastManagerVersion = "1.0.0"
         androidXCustomTabsVersion = "1.3.0"
         swipeRefreshLayoutVersion = "1.1.0"
-        billingVersion = '3.0.0'
+        billingVersion = '4.0.0'
         constraintLayoutVersion = '2.0.4'
         kotlinResultVersion = '1.1.11'
         timberVersion = "4.7.1"
diff --git a/todo.md b/todo.md
index 692398f..00783e8 100644
--- a/todo.md
+++ b/todo.md
@@ -78,15 +78,19 @@ Low priority
 
 ## DONE:
 
+Release 0.51.1 (Feb 15):
+
+ - [X] Update billing library
+
 Release 0.51:
 
 (November 9th)
 
- - [ ] Larger artwork on currently playing screen
- - [ ] Fix disappearing downloads
- - [ ] Make "mark as watched" visible even if media not started
- - [ ] Updates for open source release
- - [ ] Fix completed books not appearing as completed
+ - [X] Larger artwork on currently playing screen
+ - [X] Fix disappearing downloads
+ - [X] Make "mark as watched" visible even if media not started
+ - [X] Updates for open source release
+ - [X] Fix completed books not appearing as completed
 
 Release 0.50: