Map.Entry<K,V>#key and #value fail to infer type correctly under @StaticCompile

import groovy.transform.CompileStatic
@CompileStatic
class BrokenCompileStaticTest extends GroovyTestCase {
  void testMapForEachAttribute() {
    def result = ""
    def sum = 0
    for ( Map.Entry<String, Integer> it in [a:1, b:3].entrySet() ) {
       result += it.key
       sum += it.value
    }
    assert result == "ab"
    assert sum == 4
  }
}

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
/home/steven/BrokenCompileStaticTest.groovy: 9: [Static type checking] - Cannot find matching method int#plus(java.lang.Object <V>)
 @ line 9, column 8.
          sum += it.value
          ^

1 error