Fix Kotlin Version Mismatch After Flutter Upgrade (2025)

* What went wrong:
Execution failed for task ':app:compileDebugKotlin'.
> e: This version of the Kotlin compiler is incompatible with the specified JVM target '1.8'.
Please specify a supported JVM target version.

* What went wrong:
The Android Gradle plugin supports only Kotlin Gradle plugin version 1.8.0 and higher.
Your project is using version 1.7.10.
Please switch to a supported version of the Kotlin Gradle plugin.

Let's get this sorted out. We'll walk through the process of manually aligning your project's Android build configuration with your new Flutter version's requirements.

Step 1: Consult the Oracle (Flutter Release Notes)

Your first and most important stop should always be the official Flutter release notes or the Android Gradle Plugin documentation. This is the source of truth. For a hypothetical Flutter 4.0 release in early 2025, the documentation would specify the compatible versions. For this guide, let's assume the new requirements are:

• Android Gradle Plugin (AGP): 8.3.1
• Gradle: 8.4
• Kotlin: 1.9.22

With these target versions in mind, we can now update our files.

Step 2: Update Your Project's Kotlin Version

This is the most common part of the fix. You need to define the Kotlin version for your entire Android project.

Open your project-level Gradle file located at android/build.gradle.

Look for the buildscript block at the top. Inside it, you'll find an ext block where the kotlin_version is defined. Update this version to the one required.

// In android/build.gradle

buildscript {
    // Previous version might be ext.kotlin_version = '1.7.10'
    ext.kotlin_version = '1.9.22' // <-- UPDATE THIS LINE
    repositories {
        google()
        mavenCentral()
    }

    dependencies {
        // ... other dependencies
    }
}

Step 3: Align the Android Gradle Plugin (AGP)

In the same android/build.gradle file, inside the buildscript block, you'll find the dependency for the Android Gradle Plugin. Update its version to match the required one.

// In android/build.gradle

buildscript {
    ext.kotlin_version = '1.9.22'
    repositories {
        google()
        mavenCentral()
    }

    dependencies {
        // Previous version might be 'com.android.tools.build:gradle:7.3.0'
        classpath 'com.android.tools.build:gradle:8.3.1' // <-- UPDATE THIS LINE
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

Step 4: Tame the Gradle Wrapper

The AGP version you just set requires a specific version of Gradle itself. You update this in the Gradle Wrapper properties file.

Open the file located at android/gradle/wrapper/gradle-wrapper.properties.

Find the distributionUrl and update the Gradle version in the URL.

# In android/gradle/wrapper/gradle-wrapper.properties

...
distributionBase=GRADLE_USER_HOME
distributionPath=wrapper/dists
zipStoreBase=GRADLE_USER_HOME
zipStorePath=wrapper/dists

# Previous URL might have been gradle-7.5-all.zip
distributionUrl=https://services.gradle.org/distributions/gradle-8.4-all.zip // <-- UPDATE THIS LINE

Here's a handy reference table for common AGP, Gradle, and Kotlin version compatibilities you might encounter in 2024-2025:

AGP Version	Required Gradle Version	Recommended Kotlin Version
8.3.x	8.4+	1.9.22
8.2.x	8.2+	1.9.20
8.1.x	8.0+	1.8.20
8.0.x	8.0+	1.8.10

Note: Always refer to the official Android documentation for the most up-to-date compatibility matrix.

Step 5: The Final Cleanse: Clean & Rebuild

With all the versions updated, the last step is to clear out any old build artifacts and caches that could interfere with the new configuration. Run the following commands in your terminal from the root of your Flutter project:

flutter clean
flutter pub get

The first command removes the build/ directory and other transient files. The second ensures all your Dart and Flutter dependencies are correctly fetched.

Now, try building your app again:

flutter run

This time, Gradle will download the new wrapper version (if it hasn't already), and your build should proceed smoothly with all the compatible tools working in harmony. Success!

Going Pro: Preventing Future Version Headaches

Fixing the problem is great, but avoiding it is even better. Here are a few habits to adopt for smoother Flutter upgrades:

• Read the Release Notes: Before you even run flutter upgrade, skim the release notes on the Flutter website. They often have a dedicated section for breaking changes or required migration steps, including build tool versions.
• Use dart fix: The Flutter team is always improving automated migration tools. After upgrading, run dart fix --apply. It can often catch and fix some (though not always all) of these configuration changes automatically.
• Version Control is Your Savior: Always commit your changes before starting an upgrade. If anything goes horribly wrong, you can easily revert back to a working state with git checkout . or git stash.
• Regularly Update Dependencies: Don't wait for a major Flutter upgrade to update your packages and native configurations. Keeping things reasonably up-to-date can make major jumps less painful.

Conclusion: Back to Building

A Kotlin version mismatch after a Flutter upgrade can feel like a major roadblock, but it's really just a signpost telling you to sync up your native build tools. By methodically updating the Kotlin version, Android Gradle Plugin, and Gradle Wrapper, you can resolve the conflict quickly and reliably.

Remember the core steps: check the docs, update android/build.gradle, update gradle-wrapper.properties, and then clean your project. By making this checklist a part of your upgrade process, you'll turn a moment of frustration into a minor, predictable maintenance task. Now, go enjoy those new Flutter features!