Gradle, Java plugin, Jar MANIFEST, Class-Path is empty

I struggled with with the jar MANIFEST file built with Gradle containing an empty Class-Path. I traced down the problem to the order of the dependencies and jar blocks in the build.gradle file:

Wrong (jar before dependencies):

jar {
    manifest.attributes(
            // Class-Path won't contain "guava-15.0.jar"
            'Class-Path': configurations.runtime.files.collect { it.name }.join(' ')
    )
}

repositories {
    mavenCentral()
}

dependencies {
    compile group: 'com.google.guava', name: 'guava', version: '15.0'
}

Correct (jar after dependencies):

repositories {
    mavenCentral()
}

dependencies {
    compile group: 'com.google.guava', name: 'guava', version: '15.0'
}

jar {
    manifest.attributes(
            // results in "Class-Path: guava-15.0.jar"
            'Class-Path': configurations.runtime.files.collect { it.name }.join(' ')
    )
}