diff --git a/mobile/Makefile b/mobile/Makefile
index 9a9e82e9..3717d754 100644
--- a/mobile/Makefile
+++ b/mobile/Makefile
@@ -3,7 +3,9 @@
 # host tool remote-slot (dotfiles, ~/.local/bin). The environment, gitignored files, and make's own
 # flags do not cross, and every output (installs, archives, receipts) stays on that host. GitHub
 # Actions jobs already run on the Mac their workflow picked.
-APPLE_BUILD_HOST := haiku-7
+ifeq ($(filter command line,$(origin APPLE_BUILD_HOST))$(GITHUB_ACTIONS),)
+APPLE_BUILD_HOST := $(or $(shell remote-slot apple-host),$(error remote-slot apple-host named no Mac build host; update the dotfiles host tool remote-slot or pass APPLE_BUILD_HOST))
+endif
 ifeq ($(filter $(APPLE_BUILD_HOST),$(shell hostname -s))$(GITHUB_ACTIONS),)
 APPLE_BUILD_HOST_VARIABLES := $(strip $(foreach variable,$(sort $(.VARIABLES)),$(if $(filter command line,$(origin $(variable))),'$(variable)=$(subst ','\'',$(value $(variable)))')))
 .DEFAULT_GOAL := apple-build-host
diff --git a/mobile/README.md b/mobile/README.md
index 87eac690..dd61baf4 100644
--- a/mobile/README.md
+++ b/mobile/README.md
@@ -69,10 +69,10 @@ and the exports built on them) starts with `signing-session`, which runs the
 dotfiles host tool `build-keychain unlock`, so it signs from a fresh
 noninteractive SSH session.
 
-`haiku-7` runs every lane in `mobile/Makefile`. From any other host, `make -C mobile <lane>`
-forwards the goals and command-line variables to the dotfiles host tool `remote-slot`, which
-mirrors this checkout's exact bytes into a warm `.worktrees/remote-slot-<n>` on `haiku-7` and runs
-the lane there; its outputs stay on `haiku-7`.
+The Mac build host that `remote-slot apple-host` names runs every lane in `mobile/Makefile`. From
+any other host, `make -C mobile <lane>` forwards the goals and command-line variables to the
+dotfiles host tool `remote-slot`, which mirrors this checkout's exact bytes into a warm
+`.worktrees/remote-slot-<n>` on that host and runs the lane there; its outputs stay on that host.
 
 These lanes require the matching Developer ID or Apple Distribution identities,
 profiles, a valid `csweb` App Store Connect profile, and signed agreements for