Undefined Reference to vTable for constructor and destructor

I have a virtual base class, called AbstractHeap. AbstractHeap has a virtual function, "comp". It also has a (non-virtual) constructor and destructor that should be used by all derived classes, which are implemented.

AbstractHeap is inherited by MinHeap. It implements "comp". It also has a constructor, which just calls the base constructor.

Finally, Main.cpp just creates an instance of MinHeap.

When I compile the program, it gives me this error:

$ rm *.o && make
g++ -std=c++11 -c -g AbstractHeap.cpp
g++ -std=c++11 -c -g Main.cpp
g++ -std=c++11 -g -Wall Main.o AbstractHeap.o -o Main
Main.o: In function `MinHeap::MinHeap(int, int)':
/mnt/c/dev/Data_Structures/Lab7/MinHeap.h:8: undefined reference to `vtable for MinHeap'
/mnt/c/dev/Data_Structures/Lab7/MinHeap.h:8: undefined reference to `vtable for MinHeap'
collect2: error: ld returned 1 exit status
Makefile:2: recipe for target 'Main' failed
make: *** [Main] Error 1
owen@MatrixSword:/mnt/c/dev/Data_Structures/Lab7$ rm *.o && make
g++ -std=c++11 -c -g AbstractHeap.cpp
g++ -std=c++11 -c -g Main.cpp
g++ -std=c++11 -g -Wall Main.o AbstractHeap.o -o Main
Main.o: In function `MinHeap::MinHeap(int, int)':
MinHeap.h:8: undefined reference to `vtable for MinHeap'
MinHeap.h:8: undefined reference to `vtable for MinHeap'
Main.o: In function `MinHeap::~MinHeap()':
MinHeap.h:5: undefined reference to `vtable for MinHeap'
MinHeap.h:5: undefined reference to `vtable for MinHeap'
collect2: error: ld returned 1 exit status
Makefile:2: recipe for target 'Main' failed
make: *** [Main] Error 1

I've looked at this highly upvoted question, but it seems that the problem and solution involved QT, which I am not using.

Here's the code.

AbstractHeap.h

#ifndef ABSTRACT_HEAP_H
#define ABSTRACT_HEAP_H
#include <iostream>
#include <string>
using namespace std;

struct Item
{
    int key = -1;
    string data = "";
};

class AbstractHeap
{
    private:
        int k; //A k-heap.
        int size;
        Item* A; //The array.

    public:
        AbstractHeap(int k, int size);
        ~AbstractHeap();

        //Comparison operator. Can be interpretted as c comp b. So, if you want a <, comp is a<b. If the result is true, a has a higher priority than b.
        virtual bool comp(int a, int b) = 0;
};

#endif

AbstractHeap.cpp

#include "AbstractHeap.h"
#include <iostream>
#include <algorithm>
using namespace std;

AbstractHeap::AbstractHeap(int _k, int _size)
{
    size = _size;
    k = _k;
    A = new Item[size];
}

AbstractHeap::~AbstractHeap()
{
    delete [] A;
}

MinHeap.h

#ifndef MIN_HEAP_H
#define MIN_HEAP
#include "AbstractHeap.h"

class MinHeap : virtual public AbstractHeap
{
    public:
        MinHeap(int k, int size) : AbstractHeap{k, size} {};
        bool comp(int a, int b);
};

#endif

MinHeap.cpp

#include "MinHeap.h"

bool MinHeap::comp(int a, int b)
{
    return a < b;
}

Finally, here's my Makefile, in the unlikely event it is a result of poor Makefile writing.

Main: AbstractHeap.o Main.o 
    g++ -std=c++11 -g -Wall Main.o AbstractHeap.o -o Main

Main.o: Main.cpp
    g++ -std=c++11 -c -g Main.cpp

AbstractHeap.o: AbstractHeap.cpp AbstractHeap.h MinHeap.cpp MinHeap.h
    g++ -std=c++11 -c -g AbstractHeap.cpp