How can i implement two JNI methods with same name but different Params?

I have a java class with two native functions with same names but different parameters.

package com.example;

public class Test {

    static {
        System.loadLibrary("TestLib");
    }

    public static native void doSomething(int a);
    public static native void doSomething(int a, long b);
}

My header file looks like

#include <jni.h>

#ifndef _TEST_LIB_H_
#define _TEST_LIB_H_

#ifdef __cplusplus
extern "C" {
#endif

JNIEXPORT void JNICALL Java_com_example_Test_doSomething
    (JNIEnv *env, jclass clazz, jint a);

JNIEXPORT void JNICALL Java_com_example_Test_doSomething
    (JNIEnv *env, jclass clazz, jint a, jlong b);

#ifdef __cplusplus
}
#endif

#endif //_TEST_LIB_H_

and my cpp file

#include "TestLib.h"

JNIEXPORT void JNICALL Java_com_example_Test_doSomething
    (JNIEnv *env, jclass clazz, jint a){
    Java_com_example_Test_doSomething(env, clazz, a, -1);
}

JNIEXPORT void JNICALL Java_com_example_Test_doSomething
    (JNIEnv *env, jclass clazz, jint a, jlong b) {
    // implementation
}

with only one function it works, but after add a second one with same name and different parameters I get an error:

error: conflicting declaration of C function 'void Java_com_example_Test_doSomething(JNIEnv*, jclass, jint, jlong)'
note: previous declaration 'void Java_com_example_Test_doSomething(JNIEnv*, jclass, jint)'

I'm using android studio and experimental gradle plugin. What am I doing wrong?