diff --git a/android/KMAPro/kMAPro/build.gradle b/android/KMAPro/kMAPro/build.gradle
index 864fb36ee9..705fb17a1c 100644
--- a/android/KMAPro/kMAPro/build.gradle
+++ b/android/KMAPro/kMAPro/build.gradle
@@ -11,6 +11,12 @@ apply from: "$rootPath/version.gradle"
 
 String tier = new File('../../TIER.md').getText('UTF-8').trim();
 
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
 android {
     compileSdk 34
     namespace="com.tavultesoft.kmapro"
@@ -24,11 +30,6 @@ android {
         buildConfig = true
     }
 
-    compileOptions {
-        sourceCompatibility = JavaVersion.VERSION_21
-        targetCompatibility = JavaVersion.VERSION_21
-    }
-
     defaultConfig {
         applicationId "com.tavultesoft.kmapro"
         minSdkVersion 21
diff --git a/android/KMEA/app/build.gradle b/android/KMEA/app/build.gradle
index dd4251025b..da7191ad5c 100644
--- a/android/KMEA/app/build.gradle
+++ b/android/KMEA/app/build.gradle
@@ -12,6 +12,12 @@ base {
     archivesName = "keyman-engine"
 }
 
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
 android {
     compileSdk 34
     namespace "com.keyman.engine"
@@ -21,11 +27,6 @@ android {
         buildConfig = true
     }
 
-    compileOptions {
-        sourceCompatibility = JavaVersion.VERSION_21
-        targetCompatibility = JavaVersion.VERSION_21
-    }
-
     defaultConfig {
         minSdkVersion 21
         targetSdkVersion 34
diff --git a/android/Samples/KMSample1/app/build.gradle b/android/Samples/KMSample1/app/build.gradle
index cc92dee298..025dd366f0 100644
--- a/android/Samples/KMSample1/app/build.gradle
+++ b/android/Samples/KMSample1/app/build.gradle
@@ -2,6 +2,12 @@ plugins {
     id 'com.android.application'
 }
 
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
 android {
     compileSdk 34
     namespace="com.keyman.kmsample1"
diff --git a/android/Samples/KMSample2/app/build.gradle b/android/Samples/KMSample2/app/build.gradle
index cd2f4d6225..472a70a1b4 100644
--- a/android/Samples/KMSample2/app/build.gradle
+++ b/android/Samples/KMSample2/app/build.gradle
@@ -2,6 +2,12 @@ plugins {
     id 'com.android.application'
 }
 
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
 android {
     compileSdk 34
     namespace="com.keyman.kmsample2"
diff --git a/android/Tests/KeyboardHarness/app/build.gradle b/android/Tests/KeyboardHarness/app/build.gradle
index ab8066393b..69be625d85 100644
--- a/android/Tests/KeyboardHarness/app/build.gradle
+++ b/android/Tests/KeyboardHarness/app/build.gradle
@@ -5,6 +5,12 @@ plugins {
 ext.rootPath = '../../../'
 apply from: "$rootPath/version.gradle"
 
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
 android {
     compileSdk 34
     namespace="com.keyman.android.tests.keyboardHarness"
diff --git a/oem/firstvoices/android/app/build.gradle b/oem/firstvoices/android/app/build.gradle
index 8a6558aa3d..468517061d 100644
--- a/oem/firstvoices/android/app/build.gradle
+++ b/oem/firstvoices/android/app/build.gradle
@@ -7,6 +7,12 @@ plugins {
 ext.rootPath = '../../../../android'
 apply from: "$rootPath/version.gradle"
 
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
 android {
     compileSdk 34
     namespace="com.firstvoices.keyboards"