How to fix a "destination with the same identifier" warning with subequations?

Question

When compiling the following document (a minimal failing example):

\documentclass[a4paper,12pt]{book}                                                                                                     
\usepackage[T1]{fontenc}                                                                                                               
\usepackage[utf8]{inputenc}                                                                                                            

\usepackage{hyperref}                                                                                                   
\usepackage{amsmath}                                                                                                                   

\author{AUTHOR}                                                                                                                        
\title{TITLE}                                                                                                                          

\begin{document}                                                                                                                       
\frontmatter                                                                                                                           

\maketitle                                                                                                                             

\tableofcontents                                                                                                                       

\mainmatter                                                                                                                            

\begin{subequations}                                                                                                                   
\begin{equation}                                                                                                                       
  a = 1                                                                                                                                
\end{equation}                                                                                                                         
\begin{equation} \label{my_label}                                                                                                      
  b = 2                                                                                                                                
\end{equation}                                                                                                                         
\end{subequations}                                                                                                                     

\appendix                                                                                                                              

\backmatter                                                                                                                            
\end{document}

I got the following pdfTeX warning:

pdfTeX warning (ext4): destination with the same identifier
(name{equation.0.0.1}) has been already used, duplicate ignored

How to get rid of the warning? I do not thing the page numbering is an issue. The \numberwithin{}{} soultion neither works.

Answer 1

Inspired by package import order in Hyperlinking problems when using subequations, hyperref and cleveref I have decided to change my imports to:

\usepackage{amsmath}
\usepackage{hyperref}

It did the trick.