C++ Undefined reference to destructor? - c++

Question

I'm trying to code a game with Allegro 4 and I've hit a weird bump. The linker is claiming an undefined reference to the destructor in two of my classes, but I've done nothing with it. What could be the issue? Here is my code:
Entity.h:
#pragma once
#include <allegro.h>
struct Rectangle
{
int x;
int y;
int w;
int h;
};
typedef enum {
FACE,
POOP
} EntityType;
class Entity
{
private:
EntityType m_EntityType;
BITMAP *m_Sprite;
int m_Score;
int m_X;
int m_Y;
Rectangle *m_Hitbox;
public:
Entity();
virtual ~Entity() {destroy_bitmap(m_Sprite);}
BITMAP *GetSprite() {return m_Sprite;}
int GetScore() {return m_Score;}
int GetX() {return m_X;}
int GetY() {return m_Y;}
Rectangle GetHitbox() {return *m_Hitbox;}
void SetSprite(EntityType type);
void SetScore(int value) {m_Score = value;}
void SetX(int value) {m_X = value;}
void SetY(int value) {m_Y = value;}
void SetHitbox(EntityType type);
};
Entity.cpp:
#include "Entity.h"
void Entity::SetSprite(EntityType type)
{
if (type == FACE)
m_Sprite = load_bitmap("face.bmp", NULL);
else if (type == POOP)
m_Sprite = load_bitmap("poop.bmp", NULL);
}
void Entity::SetHitbox(EntityType type)
{
if (type == FACE)
{
GetHitbox().x = m_X;
GetHitbox().y = m_Y;
GetHitbox().w = m_X + 32;
GetHitbox().h = m_Y + 32;
}
else if (type == POOP)
{
GetHitbox().x = m_X;
GetHitbox().y = m_Y;
GetHitbox().w = m_X + 16;
GetHitbox().h = m_Y + 16;
}
}