diff --git a/build-flags.gradle b/build-flags.gradle
index be7edf7..445e9d5 100644
--- a/build-flags.gradle
+++ b/build-flags.gradle
@@ -42,3 +42,7 @@ if (!projectsWithFlags('java').isEmpty()) {
     apply from: "${libDir}/java-versionprops.gradle"
     apply from: "${libDir}/java-publish.gradle"
 }
+
+if (!projectsWithFlags('kotlin').isEmpty()) {
+    apply from: "${libDir}/kotlin.gradle"
+}
diff --git a/lib/common-dependencies.gradle b/lib/common-dependencies.gradle
index ea5fb52..6592fc2 100644
--- a/lib/common-dependencies.gradle
+++ b/lib/common-dependencies.gradle
@@ -3,7 +3,7 @@ import org.yaml.snakeyaml.Yaml
 buildscript {
     repositories {
         mavenCentral()
-        jcenter()
+        gradlePluginPortal()
     }
 
     dependencies {
@@ -76,7 +76,7 @@ configure(dependencyManagementProject) {
     apply plugin: com.github.benmanes.gradle.versions.VersionsPlugin
 
     repositories {
-        jcenter()
+        google()
         // Since we manage plugin versions here too.
         gradlePluginPortal()
         mavenCentral()
diff --git a/lib/java-rpc-proto.gradle b/lib/java-rpc-proto.gradle
index a3d59a2..18f77ce 100644
--- a/lib/java-rpc-proto.gradle
+++ b/lib/java-rpc-proto.gradle
@@ -111,6 +111,13 @@ configure(projectsWithFlags('java')) {
                 if (processResourcesTask != null) {
                     processResourcesTask.dependsOn(task)
                 }
+
+                def sourcesJarTask = tasks.findByName(sourceSet.getTaskName('sources', 'jar'))
+                if (sourcesJarTask) {
+                    // A workaround for 'sourcesJar' uses this output of task ':generateProto' without
+                    // declaring an explicit or implicit dependency.
+                    sourcesJarTask.dependsOn(task)
+                }
                 project.ext.getGenerateSourcesTask().dependsOn(task)
             }
         }
diff --git a/lib/java-rpc-thrift.gradle b/lib/java-rpc-thrift.gradle
index 1b763a7..f8c4762 100644
--- a/lib/java-rpc-thrift.gradle
+++ b/lib/java-rpc-thrift.gradle
@@ -22,6 +22,11 @@ configure(projectsWithFlags('java')) {
                 description: "Compiles the ${sourceSet.name} .thrift files."
         ])
 
+        def sourcesJarTask = project.tasks.findByName(sourceSet.getTaskName('sources', 'jar'))
+        if (sourcesJarTask) {
+            sourcesJarTask.dependsOn(task)
+        }
+
         // Use afterEvaluate to give subprojects a chance to override the properties.
         project.afterEvaluate {
             def srcDirs = project.findProperty(sourceSet.getTaskName('', 'thriftSrcDirs'))
diff --git a/lib/java-versionprops.gradle b/lib/java-versionprops.gradle
index 4c5e24d..dc404df 100644
--- a/lib/java-versionprops.gradle
+++ b/lib/java-versionprops.gradle
@@ -40,5 +40,6 @@ configure(projectsWithFlags('java', 'publish')) {
     }
 
     // Ensure version.properties is available during the build.
+    tasks.sourcesJar.dependsOn(tasks.versionProperties)
     tasks.processResources.dependsOn(tasks.versionProperties)
 }
diff --git a/lib/java.gradle b/lib/java.gradle
index 12cac3b..1262dc6 100644
--- a/lib/java.gradle
+++ b/lib/java.gradle
@@ -57,6 +57,12 @@ configure(projectsWithFlags('java')) {
         sourceSet.java.srcDir file("${project.ext.genSrcDir}/${sourceSet.name}/java")
         sourceSet.resources.srcDir file("${project.ext.genSrcDir}/${sourceSet.name}/resources")
     }
+    afterEvaluate {
+        Task generateSourcesTask = project.tasks.findByName('generateSources')
+        if (generateSourcesTask != null) {
+            tasks.sourcesJar.dependsOn(generateSourcesTask)
+        }
+    }
 
     java {
         withJavadocJar()
diff --git a/lib/kotlin.gradle b/lib/kotlin.gradle
new file mode 100644
index 0000000..a25546b
--- /dev/null
+++ b/lib/kotlin.gradle
@@ -0,0 +1,35 @@
+configure(projectsWithFlags('kotlin')) {
+
+    apply plugin: 'kotlin'
+    apply plugin: "org.jlleitschuh.gradle.ktlint"
+
+    def target = "1.8"
+    def compilerArgs = ["-Xjsr305=strict", "-java-parameters"]
+    compileKotlin {
+        kotlinOptions.jvmTarget = target
+        kotlinOptions.freeCompilerArgs = compilerArgs
+    }
+    compileTestKotlin {
+        kotlinOptions.jvmTarget = target
+        kotlinOptions.freeCompilerArgs = compilerArgs
+    }
+
+    ktlint {
+        // https://github.com/pinterest/ktlint/issues/764
+        version.set("0.36.0")
+        verbose.set(true)
+        reporters {
+            reporter "html"
+        }
+        // https://github.com/pinterest/ktlint/issues/527
+        disabledRules = ["import-ordering"]
+
+        filter {
+            exclude("**/gen-src/**")
+        }
+    }
+
+    // A workaround for 'runKtlintCheckOverMainSourceSet' uses this output of task ':generateProto' without
+    // declaring an explicit or implicit dependency.
+    tasks.runKtlintCheckOverMainSourceSet.dependsOn(project.ext.getGenerateSourcesTask())
+}