Kotlin Error: Module was compiled with incompatible version – solution

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"Module was compiled with an incompatible version of Kotlin" — how I beat this error and you can too

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Have you ever felt like Sherlock Holmes trying to understand a mysterious compiler message? If you work with Kotlin, you've probably encountered this Frankenstein monster: "Module was compiled with an incompatible version of Kotlin. The binary version of its metadata is 1.5.1, expected version is 1.1.15". Thousands of developers on Stack Overflow have puzzled over this error. And so did I.

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Imagine: you updated your dependencies, clicked "Run" and... bam! Your project refuses to build, and this message is displayed in the console. Sound familiar? Let's figure out why this happens and how to make your code work.

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Why the error occurs: a brief primer

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Kotlin is a language that is actively evolving. Each new version brings improvements, but along with them — compatibility issues. The essence of the error is simple: you are using a library (module) that was compiled for one version of Kotlin (in our case, 1.5.1), while your project expects another (1.1.15). It's like trying to put a SIM card from an iPhone 14 into a Nokia 3310 — it physically doesn't fit.

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The incompatible version of Kotlin error usually occurs in projects where:

Android Studio or IntelliJ IDEA is used
Dependency management is done via Gradle
Third-party libraries or modules are connected
The Kotlin plugin version and Kotlin stdlib version do not match

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Let's look at three most effective ways to solve the problem. We'll move from the simplest to the most reliable.

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Method #1: Synchronize Kotlin versions (the most obvious)

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The first thing to do is to check that all components of your project use the same version of Kotlin. It's like tuning an orchestra: all instruments must play in the same key.

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Step 1: Check the Kotlin plugin version

Open the build.gradle file (project level) and find the buildscript section. Make sure the plugin version matches your expectations:

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// build.gradle (Project level)\nbuildscript {\n    ext.kotlin_version = '1.5.1' // or your version\n    repositories {\n        google()\n        mavenCentral()\n    }\n    dependencies {\n        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"\n        // other dependencies\n    }\n}

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Step 2: Check the version in the app module

Now look into your module's build.gradle (usually app). The Kotlin version should also be specified there:

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// build.gradle (Module: app)\napply plugin: 'com.android.application'\napply plugin: 'kotlin-android'\n\nandroid {\n    // ... Android configuration\n}\n\ndependencies {\n    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"\n    // other dependencies\n}

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Step 3: Sync Gradle

After changing the versions, be sure to click Sync Now in Android Studio. This will update all dependencies. If the error was caused by a simple desynchronization, it will disappear.

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💡 Pro tip: If you use the $kotlin_version variable in both files, it's enough to change it in just one place. This reduces the risk of errors.

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Method #2: Clean the cache and rebuild the project

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Sometimes Gradle caches old versions of libraries. Even if you've fixed everything in the configuration, it may stubbornly pull the old version. It's like an old browser cache — you need to clear it.

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