diff --git a/aedile-core/src/main/kotlin/com/sksamuel/aedile/core/builders.kt b/aedile-core/src/main/kotlin/com/sksamuel/aedile/core/builders.kt
index b2e73a0..41a10d8 100644
--- a/aedile-core/src/main/kotlin/com/sksamuel/aedile/core/builders.kt
+++ b/aedile-core/src/main/kotlin/com/sksamuel/aedile/core/builders.kt
@@ -20,7 +20,7 @@ import java.util.concurrent.Executor
  * If the suspendable computation throws or computes a null value then the
  * entry will be automatically removed.
  */
-fun <K, V> Caffeine<Any, Any>.asCache(): Cache<K, V> {
+fun <K : Any?, V : Any?> Caffeine<in K, in V>.asCache(): Cache<K, V> {
    val scope = CoroutineScope(Dispatchers.IO + CoroutineName("Aedile-AsyncLoadingCache-Scope") + SupervisorJob())
    return asCache(scope)
 }
@@ -34,7 +34,7 @@ fun <K, V> Caffeine<Any, Any>.asCache(): Cache<K, V> {
  * If the suspendable computation throws or computes a null value then the
  * entry will be automatically removed.
  */
-fun <K, V> Caffeine<Any, Any>.asCache(scope: CoroutineScope): Cache<K, V> {
+fun <K : Any?, V : Any?> Caffeine<in K, in V>.asCache(scope: CoroutineScope): Cache<K, V> {
    return Cache(scope, true, buildAsync())
 }
 
diff --git a/aedile-core/src/test/kotlin/com/sksamuel/aedile/core/AsCacheTest.kt b/aedile-core/src/test/kotlin/com/sksamuel/aedile/core/AsCacheTest.kt
index 266350d..3df8b26 100644
--- a/aedile-core/src/test/kotlin/com/sksamuel/aedile/core/AsCacheTest.kt
+++ b/aedile-core/src/test/kotlin/com/sksamuel/aedile/core/AsCacheTest.kt
@@ -1,10 +1,12 @@
 package com.sksamuel.aedile.core
 
 import com.github.benmanes.caffeine.cache.Caffeine
+import com.github.benmanes.caffeine.cache.Expiry
 import io.kotest.assertions.throwables.shouldThrow
 import io.kotest.core.spec.style.FunSpec
 import io.kotest.matchers.shouldBe
 import kotlinx.coroutines.delay
+import org.checkerframework.checker.index.qual.NonNegative
 
 class AsCacheTest : FunSpec() {
    init {
@@ -110,5 +112,37 @@ class AsCacheTest : FunSpec() {
          cache.contains("wibble") shouldBe true
          cache.contains("bubble") shouldBe false
       }
+
+      test("check invariants on expire after") {
+         val loggerExpiry = object : Expiry<Int, String> {
+            override fun expireAfterRead(
+               key: Int?,
+               value: String?,
+               currentTime: Long,
+               currentDuration: @NonNegative Long
+            ): Long {
+               return 0
+            }
+
+            override fun expireAfterCreate(key: Int?, value: String?, currentTime: Long): Long {
+               return 0
+            }
+
+            override fun expireAfterUpdate(
+               key: Int?,
+               value: String?,
+               currentTime: Long,
+               currentDuration: @NonNegative Long
+            ): Long {
+               return 0
+            }
+         }
+
+         Caffeine.newBuilder()
+            .maximumSize(2000)
+            .initialCapacity(500)
+            .expireAfter(loggerExpiry)
+            .asCache<Int, String>()
+      }
    }
 }