John Källén’s answer was correct, but in my case I had an end point defined so setting the maxReceivedMessageSize had to be as follows:
<standardEndpoints>
<webHttpEndpoint>
<standardEndpoint name=""
helpEnabled="true"
automaticFormatSelectionEnabled="true"
maxReceivedMessageSize="2147483647">
</standardEndpoint>
</webHttpEndpoint>
</standardEndpoints>