diff --git a/build.gradle b/build.gradle
index 22baf2c..a99079b 100644
--- a/build.gradle
+++ b/build.gradle
@@ -3,6 +3,10 @@ plugins {
     id 'org.openjfx.javafxplugin' version '0.1.0'
 }
 
+repositories {
+    mavenCentral()
+}
+
 java {
     toolchain {
         languageVersion = JavaLanguageVersion.of(21)
diff --git a/gradle.properties b/gradle.properties
new file mode 100644
index 0000000..1bedc76
--- /dev/null
+++ b/gradle.properties
@@ -0,0 +1,4 @@
+# Pin Gradle daemon JVM to Java 21 (system default may be 25 which is unsupported by Gradle 8.9).
+# To build: JAVA_HOME=/usr/lib/jvm/openjdk-bin-21 ./gradlew jar
+# Or install Gradle 8.13+ which supports Java 25.
+org.gradle.java.home=/usr/lib/jvm/openjdk-bin-21