Duplicate class Android Origin: On your device Last updated 13 Oct 2026

Duplicate class X found in modules A and B

Two dependencies ship the same class — typically old Android Support libraries mixed with AndroidX, or Kotlin stdlib-jdk7/jdk8 version mixes.

Exact message you may see Duplicate classfound in modulesDuplicate class kotlin.collections
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Seen on: Android

Meaning

The build merges all classes into one app; the same fully-qualified class in two artifacts is a conflict. The message names both modules, which tells you exactly which dependency to exclude or upgrade.

Common causes

  • Mixing com.android.support with AndroidX
  • Different Kotlin stdlib artifacts (kotlin-stdlib-jdk8 vs kotlin-stdlib) on mismatched versions
  • Two libraries bundling the same third-party code (Guava listenablefuture, protobuf-lite vs protobuf-java)

⚡ Quick fix

  1. Enable Jetifier / migrate to AndroidX
  2. Align Kotlin versions with the Kotlin BOM
  3. Exclude the duplicate module from one dependency
  4. Run ./gradlew app:dependencies to find who brings it in

Detailed fix by platform

Android

  1. Align Kotlin and exclude a duplicate:
    kotlin
    dependencies {
    implementation(platform("org.jetbrains.kotlin:kotlin-bom:1.9.24"))
    implementation("com.example:legacy-lib:2.0") {
        exclude(group = "com.google.guava", module = "listenablefuture")
    }
}

How to diagnose

  1. Modules — Which two artifacts are named?
  2. Tree — gradlew dependencies — who pulls each in?
  3. Versions — Can one upgrade remove the conflict?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: On your device. Errors that are often confused with or caused by this one (click to open):

0x8007007E — 0x8007007E: The specified module could not be found (Windows)0x8007007EAndroid resource linking failed — AAPT: error: resource x (aka y) not found — Android resource linking failed (Android)Android resource link…android:attr/lStar not found — AAPT: error: resource android:attr/lStar not found (Android)android:attr/lStar no…Cannot fit requested classes in a single dex file — Cannot fit requested classes in a single dex file (# methods: 65536 > 65536) — mergeDex failed (Android)Cannot fit requested …ClassNotFoundException — java.lang.ClassNotFoundException / NoClassDefFoundError (Java)ClassNotFoundExceptionComposer conflict — Your requirements could not be resolved to an installable set of packages. (PHP)Composer conflictCould not resolve — Gradle: Could not resolve all files for configuration / Could not resolve dependency (Android)Could not resolveDependency requires compileSdk — Dependency 'androidx.x:1.y' requires libraries and applications that depend on it to compile against version 34 or later of the Android APIs (Android)Dependency requires c…Duplicate…

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