If you happen to be using DragonFly from a network location that only allows http/https as outbound traffic, you won’t be able to update /usr/src using defaults. /usr/Makefile pulls DragonFly source using a git:// URL.
The fix is to use the read-only Github mirror. You can set origin manually or just change GITHOST in /usr/Makefile (or GITURL_SRC if you are on DragonFly-master) to “https://github.com/DragonFlyBSD/DragonFlyBSD”.
(Guess what I did today? Updated to note it’s different on -master. Thanks tuxillo for reminding me of this whole thing.)