Porting Arduino code to AVR/C++ input not working?

So. I'm trying to read an input on the Arduino Nano using C++/AVR/Eclipse instead of the regular arduino IDE. The code below is working in the arduino IDE

void setup() {
  // put your setup code here, to run once:
  pinMode(13, OUTPUT);
  pinMode(5, INPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  if(digitalRead(5)){
    digitalWrite(13,1);
  }else{
    digitalWrite(13,0);
  }
}

I'm porting the code to AVR/C++ in Eclipse, regular blinking leds is working... but I can't read inputs for some reason...

#define F_CPU 16000000UL //16MHz
#include <avr/io.h>
#include <util/delay.h>

#define set_bit(Y,bit_x) (Y|=(1<<bit_x))
#define clear_bit(Y,bit_x) (Y&=~(1<<bit_x))
#define isset_bit(Y,bit_x) (Y&(1<<bit_x))
#define toggle_bit(Y,bit_x) (Y^=(1<<bit_x))

int main( ){
    DDRB = 0xFF;//Setting all portB pins to output (D13/PB5 - LED)
    DDRD = 0x00;//Setting all portD pins to input  (D5 /PD5 - INPUT)

    while(1){
        if(isset_bit(PORTD,PD5)){//if input... doesn't work?
            set_bit(PORTB,PB5);//Set output (Tested to be working)
        }else{
            clear_bit(PORTB,PB5);//Clear output
        }
    }
}