How to free memory returned by glxChooseFBConfig?

Question

glxChooseFBConfig returns GLXFBConfig* and GLXFBConfig is defined this way:

typedef struct __GLXFBConfigRec *GLXFBConfig;

Here is an example function which uses glxChooseFBConfig and frees memory:

void fun()
{
    const int attribs[] =
    {
        GLX_RENDER_TYPE, GLX_RGBA_BIT,
        GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT,
        GLX_X_VISUAL_TYPE, GLX_TRUE_COLOR,
        GLX_DOUBLEBUFFER, True,
        GLX_RED_SIZE, 8,
        GLX_GREEN_SIZE, 8,
        GLX_BLUE_SIZE, 8,
        GLX_ALPHA_SIZE, 8,
        GLX_DEPTH_SIZE, 24,
        GLX_STENCIL_SIZE, 8,
        None
    };

    Display* dpy = XOpenDisplay(NULL);
    int count = 0;
    GLXFBConfig* fbconfigs = glXChooseFBConfig(dpy, DefaultScreen(dpy), attribs, &count);

    //do something with fbconfigs

    for(int i = 0; i < count; ++i)
    {
        XFree(fbconfigs[i]);
    }

    XFree(fbconfigs);
}

I compile my application with flag -fsanitize=address. When I run the application I get a sanitizer error: attempting double-free What is wrong ?