diff --git a/.github/workflows/android.yml b/.github/workflows/android.yml
index 422d38bcb..6475f79d5 100644
--- a/.github/workflows/android.yml
+++ b/.github/workflows/android.yml
@@ -24,7 +24,7 @@ permissions:
   security-events: none
   statuses: none
 env:
-  JAVA_HOME: /usr/lib/jvm/java-17-openjdk-amd64
+  JAVA_HOME: /usr/lib/jvm/java-21-openjdk-amd64
 jobs:
   build:
     runs-on: ubuntu-latest
@@ -36,10 +36,10 @@ jobs:
       - name: Fail on bad translations
         run: if grep -ri "<xliff" app/src/main/res/values*/strings.xml; then echo "Invalidly escaped translations found"; exit 1; fi
       - uses: gradle/actions/wrapper-validation@v4
-      - name: set up OpenJDK 17
+      - name: set up OpenJDK 21
         run: |
           sudo apt-get update
-          sudo apt-get install -y openjdk-17-jdk-headless
+          sudo apt-get install -y openjdk-21-jdk-headless
           sudo update-alternatives --auto java
       - name: Build
         run: ./gradlew assemble${{ matrix.flavor }}Release
diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index 97d3e5683..d34f5e0af 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -14,6 +14,10 @@ spotbugs {
     reportsDir.set(layout.buildDirectory.file("reports/spotbugs/").get().asFile)
 }
 
+kotlin {
+    jvmToolchain(21)
+}
+
 android {
     namespace = "protect.card_locker"
     compileSdk = 35
@@ -104,7 +108,11 @@ android {
         lintConfig = file("lint.xml")
     }
     kotlinOptions {
-        jvmTarget = "17"
+        jvmTarget = "21"
+    }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_21
+        targetCompatibility = JavaVersion.VERSION_21
     }
 }
 
diff --git a/build.sh b/build.sh
index 8cd9e6b99..d7168d018 100755
--- a/build.sh
+++ b/build.sh
@@ -11,13 +11,13 @@ if [ -z "${ANDROID_SDK_ROOT:-}" ]; then
 fi
 
 if [ -z "${JAVA_HOME:-}" ]; then
-  echo "JAVA_HOME is not set, setting to Java 17"
+  echo "JAVA_HOME is not set, setting to Java 21"
   if [ -f "/etc/debian_version" ]; then
-    echo "Debian-based distro, Java 17 is /usr/lib/jvm/java-17-openjdk-amd64"
-    export JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64
+    echo "Debian-based distro, Java 21 is /usr/lib/jvm/java-21-openjdk-amd64"
+    export JAVA_HOME=/usr/lib/jvm/java-21-openjdk-amd64
   else
-    echo "Not Debian-based, assuming Fedora and setting Java 17 as /usr/lib/jvm/java-17-openjdk"
-    export JAVA_HOME=/usr/lib/jvm/java-17-openjdk
+    echo "Not Debian-based, assuming Fedora and setting Java 21 as /usr/lib/jvm/java-21-openjdk"
+    export JAVA_HOME=/usr/lib/jvm/java-21-openjdk
   fi
 fi