--- a/build.gradle
+++ b/build.gradle
@@ -85,6 +85,11 @@
 
     version = parent.version
 
+    compileJava   {
+        sourceCompatibility = '1.8'
+        targetCompatibility = '1.8'
+    }
+
     ext {
         depends = [
                 guava: 'com.google.guava:guava:27.1-android',