C++ Qt Multiple Definitions

I'm trying to create a simple GUI application (so far) in Qt with C++ using the MinGW compiler. However, the compiler is informing me that I have a multiple definition of 'WiimoteScouter::WiimoteScouter(QWidget*)' on line 4 of wiimotescouter.cpp. I am using a check to make sure the header isn't included multiple times, but apparently it's not working, and I'm not sure why.

Here's the header file:

#ifndef WIIMOTESCOUTER_H
#define WIIMOTESCOUTER_H

#include <QWidget>

class QLabel;
class QLineEdit;
class QTextEdit;

class WiimoteScouter : public QWidget
{
    Q_OBJECT

public:
    WiimoteScouter(QWidget *parent = 0);

private:
    QLineEdit *eventLine;
};

#endif // WIIMOTESCOUTER_H

And here's the cpp file:

#include <QtGui>
#include "wiimotescouter.h"

WiimoteScouter::WiimoteScouter(QWidget *parent) :
    QWidget(parent)
{
    QLabel *eventLabel = new QLabel(tr("Event:"));
    eventLine = new QLineEdit;

    QGridLayout *mainLayout = new QGridLayout;
    mainLayout->addWidget(eventLabel, 0, 0);
    mainLayout->addWidget(eventLine, 0, 1);

    setLayout(mainLayout);
    setWindowTitle(tr("Wiimote Alliance Scouter"));
}

Lastly, the main.cpp:

#include <QtGui>
#include "wiimotescouter.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    WiimoteScouter wiimoteScouter;
    wiimoteScouter.show();

    return app.exec();
}

I've seen this happen before when a source file got duplicated in the project (.pro or .pri) file. Check all of the "SOURCES =" and "SOURCES +=" lines in your project file and make sure the cpp file is not in there more than once.