diff --git a/android-ech/build.gradle.kts b/android-ech/build.gradle.kts
index 698d195..61db794 100644
--- a/android-ech/build.gradle.kts
+++ b/android-ech/build.gradle.kts
@@ -1,7 +1,6 @@
 plugins {
   // AGP 9 brings Kotlin support with it — applying the Kotlin Android plugin here fails.
   alias(libs.plugins.android.library)
-  alias(libs.plugins.android.junit5)
 }
 
 // The version of OkHttp under test. This suite defaults to the snapshot rather than to the
@@ -36,22 +35,11 @@ android {
     // An AndroidJUnitRunner that calls OkHttp.initialize first. See EchTestRunner for why the
     // library's own androidx Startup initializer doesn't cover an instrumentation APK.
     testInstrumentationRunner = "okhttp.testbed.android.ech.EchTestRunner"
-    testInstrumentationRunnerArguments +=
-      mapOf(
-        // The suite is JUnit 5, as the JVM suites are.
-        "runnerBuilder" to "de.mannodermaus.junit5.AndroidJUnit5Builder",
-      )
   }
 
   compileOptions {
     sourceCompatibility(JavaVersion.VERSION_11)
     targetCompatibility(JavaVersion.VERSION_11)
-
-    // JUnit 5 is compiled against Java 8 APIs — `java.util.function`, `Optional`, `java.time` —
-    // which Android only has from API 26. The suite runs on API 21 upwards, so without this the
-    // runner dies with NoClassDefFoundError on the oldest emulators in the matrix before a single
-    // test is reached. Desugaring is what makes "minSdk 21" true of the tests as well as the code.
-    isCoreLibraryDesugaringEnabled = true
   }
 
   testOptions {
@@ -60,8 +48,6 @@ android {
 }
 
 dependencies {
-  coreLibraryDesugaring(libs.desugar.jdk.libs)
-
   androidTestImplementation("com.squareup.okhttp3:okhttp:$okhttpVersion")
   androidTestImplementation("com.squareup.okhttp3:okhttp-dnsoverhttps:$okhttpVersion")
 
@@ -72,10 +58,8 @@ dependencies {
   androidTestImplementation("com.squareup.okhttp3:okhttp-android:$okhttpVersion")
 
   androidTestImplementation(libs.assertk)
-  androidTestImplementation(libs.junit.jupiter.api)
-  androidTestImplementation(libs.junit5android.core)
+  androidTestImplementation(libs.junit4)
   androidTestImplementation(libs.androidx.test.runner)
-  androidTestRuntimeOnly(libs.junit5android.runner)
 }
 
 // `check` doesn't run instrumentation tests, so the public-API check has to be wired to the
diff --git a/android-ech/src/androidTest/kotlin/okhttp/testbed/android/ech/EncryptedClientHelloTest.kt b/android-ech/src/androidTest/kotlin/okhttp/testbed/android/ech/EncryptedClientHelloTest.kt
index 7b4c8ae..3585f47 100644
--- a/android-ech/src/androidTest/kotlin/okhttp/testbed/android/ech/EncryptedClientHelloTest.kt
+++ b/android-ech/src/androidTest/kotlin/okhttp/testbed/android/ech/EncryptedClientHelloTest.kt
@@ -36,8 +36,8 @@ import okhttp3.Request
 import okhttp3.Response
 import okhttp3.Route
 import okhttp3.dnsoverhttps.DnsOverHttps
-import org.junit.jupiter.api.Assumptions.assumeTrue
-import org.junit.jupiter.api.Test
+import org.junit.Assume.assumeTrue
+import org.junit.Test
 
 /**
  * Encrypted Client Hello, end to end, against the containers `run-ech-test.sh` starts on the
@@ -117,10 +117,10 @@ class EncryptedClientHelloTest {
 
   private fun fixture(): Fixture {
     val arguments = InstrumentationRegistry.getArguments()
-    assumeTrue(arguments.getString("ech") == "true", "requires the host-side ECH fixtures")
+    assumeTrue("requires the host-side ECH fixtures", arguments.getString("ech") == "true")
     assumeTrue(
-      Build.VERSION.SDK_INT >= TLS_13_API_LEVEL,
       "the ECH fixture origin is TLS 1.3 only, which Android has from API $TLS_13_API_LEVEL",
+      Build.VERSION.SDK_INT >= TLS_13_API_LEVEL,
     )
     val dohPort = requireNotNull(arguments.getString("dohPort")).toInt()
     val caCertificate = Base64.decode(requireNotNull(arguments.getString("caCertificate")), Base64.DEFAULT)
diff --git a/android-ech/src/androidTest/kotlin/okhttp/testbed/android/ech/PublicEncryptedClientHelloTest.kt b/android-ech/src/androidTest/kotlin/okhttp/testbed/android/ech/PublicEncryptedClientHelloTest.kt
index 40bc7e7..4fd6b7e 100644
--- a/android-ech/src/androidTest/kotlin/okhttp/testbed/android/ech/PublicEncryptedClientHelloTest.kt
+++ b/android-ech/src/androidTest/kotlin/okhttp/testbed/android/ech/PublicEncryptedClientHelloTest.kt
@@ -31,9 +31,9 @@ import okhttp3.Request
 import okhttp3.Response
 import okhttp3.Route
 import okhttp3.dnsoverhttps.DnsOverHttps
-import org.junit.jupiter.api.Assumptions.assumeTrue
-import org.junit.jupiter.api.BeforeEach
-import org.junit.jupiter.api.Test
+import org.junit.Assume.assumeTrue
+import org.junit.Before
+import org.junit.Test
 
 /**
  * [okhttp.testbed.network.EchTest]'s cases, on the one platform where they can all pass.
@@ -56,9 +56,9 @@ import org.junit.jupiter.api.Test
 class PublicEncryptedClientHelloTest {
   private lateinit var client: OkHttpClient
 
-  @BeforeEach
+  @Before
   fun setUp() {
-    assumeTrue(Build.VERSION.SDK_INT >= 37, "ECH requires Android API 37")
+    assumeTrue("ECH requires Android API 37", Build.VERSION.SDK_INT >= 37)
 
     val bootstrapClient = OkHttpClient()
 
diff --git a/build.gradle.kts b/build.gradle.kts
index c9fe74e..8abb93b 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -5,7 +5,6 @@ import org.jetbrains.kotlin.gradle.tasks.KotlinJvmCompile
 plugins {
   alias(libs.plugins.kotlin.jvm) apply false
   alias(libs.plugins.android.library) apply false
-  alias(libs.plugins.android.junit5) apply false
 }
 
 // The JDK the suites *run* on: what a user's application would be running when it calls the
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index 2c3e4f0..dd804cf 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -1,10 +1,8 @@
 [versions]
 agp = "9.3.1"
-android-junit5 = "2.0.1"
 androidx-test-runner = "1.7.0"
 assertk = "0.28.1"
-# Backports the Java 8 APIs JUnit 5 needs onto the API 21 emulators in the android-ech matrix.
-desugar-jdk-libs = "2.1.5"
+junit4 = "4.13.2"
 junit-platform = "1.14.4"
 kotlin = "2.4.10"
 # Must match the mockserver/mockserver image tag; the client refuses to talk to a
@@ -28,13 +26,11 @@ testcontainers = "2.0.5"
 [libraries]
 androidx-test-runner = { module = "androidx.test:runner", version.ref = "androidx-test-runner" }
 assertk = { module = "com.willowtreeapps.assertk:assertk", version.ref = "assertk" }
-desugar-jdk-libs = { module = "com.android.tools:desugar_jdk_libs", version.ref = "desugar-jdk-libs" }
+junit4 = { module = "junit:junit", version.ref = "junit4" }
 junit-jupiter-api = { module = "org.junit.jupiter:junit-jupiter-api", version.ref = "org-junit-jupiter" }
 junit-jupiter-engine = { module = "org.junit.jupiter:junit-jupiter-engine", version.ref = "org-junit-jupiter" }
 junit-jupiter-params = { module = "org.junit.jupiter:junit-jupiter-params", version.ref = "org-junit-jupiter" }
 junit-platform-launcher = { module = "org.junit.platform:junit-platform-launcher", version.ref = "junit-platform" }
-junit5android-core = { module = "de.mannodermaus.junit5:android-test-core", version.ref = "android-junit5" }
-junit5android-runner = { module = "de.mannodermaus.junit5:android-test-runner", version.ref = "android-junit5" }
 mockserver = { module = "org.testcontainers:testcontainers-mockserver", version.ref = "testcontainers" }
 mockserver-client = { module = "org.mock-server:mockserver-client-java-no-dependencies", version.ref = "mockserver" }
 okhttp = { module = "com.squareup.okhttp3:okhttp", version.ref = "okhttp" }
@@ -42,6 +38,5 @@ testcontainers = { module = "org.testcontainers:testcontainers", version.ref = "
 testcontainers-junit5 = { module = "org.testcontainers:testcontainers-junit-jupiter", version.ref = "testcontainers" }
 
 [plugins]
-android-junit5 = { id = "de.mannodermaus.android-junit5", version.ref = "android-junit5" }
 android-library = { id = "com.android.library", version.ref = "agp" }
 kotlin-jvm = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }
diff --git a/renovate.json b/renovate.json
index 31869b2..95ff588 100644
--- a/renovate.json
+++ b/renovate.json
@@ -5,7 +5,7 @@
   ],
   "packageRules": [
     {
-      "description": "Stay on JUnit 5. JUnit 6 requires Java 17+ and a coordinated bump of the android-junit5 plugin, so it is not a drop-in upgrade here.",
+      "description": "Keep the JVM test suites on JUnit 5. JUnit 6 requires Java 17+, so it is not a drop-in upgrade here.",
       "matchManagers": [
         "gradle"
       ],