diff --git a/build.sbt b/build.sbt
index 6bd12044c7..b9e45d644b 100644
--- a/build.sbt
+++ b/build.sbt
@@ -28,11 +28,12 @@ import org.typelevel.scalacoptions.JavaMajorVersion.javaMajorVersion
 
 // To test release candidates, find the beam repo and add it as a resolver
 // ThisBuild / resolvers += "apache-beam-staging" at "https://repository.apache.org/content/repositories/"
+ThisBuild / resolvers += "apache-beam-staging" at "https://repository.apache.org/content/repositories/orgapachebeam-1385/"
 val beamVendorVersion = "0.1"
-val beamVersion = "2.58.1"
+val beamVersion = "2.59.0"
 
 // check version used by beam
-// https://github.com/apache/beam/blob/v2.58.1/buildSrc/src/main/groovy/org/apache/beam/gradle/BeamModulePlugin.groovy
+// https://github.com/apache/beam/blob/v2.59.0-RC1/buildSrc/src/main/groovy/org/apache/beam/gradle/BeamModulePlugin.groovy
 val autoServiceVersion = "1.0.1"
 val autoValueVersion = "1.9"
 val bigdataossVersion = "2.2.16"
@@ -61,7 +62,7 @@ val googleApiServicesStorageVersion = s"v1-rev20240319-$googleClientsVersion"
 // beam tested versions
 val zetasketchVersion = "0.1.0" // sdks/java/extensions/zetasketch/build.gradle
 val avroVersion = avroCompilerVersion // sdks/java/extensions/avro/build.gradle
-val flinkVersion = "1.18.0" // runners/flink/1.17/build.gradle
+val flinkVersion = "1.18.0" // runners/flink/1.18/build.gradle
 val flinkMinorVersion = VersionNumber(flinkVersion).numbers.take(2).mkString(".")
 val hadoopVersion = "3.2.4" // sdks/java/io/parquet/build.gradle
 val sparkVersion = "3.5.0" // runners/spark/3/build.gradle
diff --git a/scio-test/core/src/main/scala/com/spotify/scio/testing/SCollectionMatchers.scala b/scio-test/core/src/main/scala/com/spotify/scio/testing/SCollectionMatchers.scala
index f7d2c91a22..2f825b408f 100644
--- a/scio-test/core/src/main/scala/com/spotify/scio/testing/SCollectionMatchers.scala
+++ b/scio-test/core/src/main/scala/com/spotify/scio/testing/SCollectionMatchers.scala
@@ -19,7 +19,6 @@ package com.spotify.scio.testing
 
 import java.lang.{Iterable => JIterable}
 import java.util.{Map => JMap}
-
 import com.spotify.scio.coders.Coder
 import com.spotify.scio.values.SCollection
 import com.twitter.chill.Externalizer
@@ -27,7 +26,7 @@ import org.apache.beam.sdk.testing.PAssert
 import org.apache.beam.sdk.testing.PAssert.{IterableAssert, SingletonAssert}
 import org.apache.beam.sdk.transforms.SerializableFunction
 import org.apache.beam.sdk.transforms.windowing.BoundedWindow
-import org.apache.beam.sdk.util.CoderUtils
+import org.apache.beam.sdk.util.{CoderUtils, SerializableSupplier}
 import org.scalatest.matchers.{MatchResult, Matcher}
 import org.{hamcrest => h}
 import org.hamcrest.Matchers
@@ -69,13 +68,10 @@ private object ScioMatchers {
   /** Create a hamcrest matcher that can be serialized using a Coder[T]. */
   private def supplierFromCoder[A: Coder, B](@transient a: A, @transient context: ScioContext)(
     builder: A => B
-  ) = {
+  ): SerializableSupplier[B] = {
     val coder = CoderMaterializer.beam(context, Coder[A])
     val encoded = CoderUtils.encodeToByteArray(coder, a)
-    new SerializableMatchers.SerializableSupplier[B] {
-      def a = CoderUtils.decodeFromByteArray(coder, encoded)
-      def get() = builder(a)
-    }
+    () => builder(CoderUtils.decodeFromByteArray(coder, encoded))
   }
 
   /**