caddy: linux arm: Invalid memory address or null pointer dereference panic when using fastcgi

This is via vanilla Caddy 0.10.5 on a Raspberry pi 3 (arm v7), running a 32 bit Arch linux. Earlier versions, such as 0.10.4 work fine.

PHP version: 7.1.7

When using FastCGI with php-fm, Caddy generates an Internal server error (http 500). Additionally, a panic is logged:

[PANIC /] /usr/local/go/src/sync/atomic/asm_linux_arm.s:109 - runtime error: invalid memory address or nil pointer dereference

Caddy file:

mysite.com {
gzip
root /var/www/mysite.com
fastcgi / /run/php-fpm/php-fpm.sock php
}