diff --git a/roles/pi_irserver/README.md b/roles/pi_irserver/README.md
index fea98a7..60e4352 100644
--- a/roles/pi_irserver/README.md
+++ b/roles/pi_irserver/README.md
@@ -3,3 +3,9 @@
 Installs and configures `irserver` (with a Hauppauge remote config) as an
 autostarted systemd service for IR remote control, and registers it with
 `pi_sysdweb`.
+
+The shipped `files/irserver` is a 32-bit ARM binary needing `libzip.so.4`, so it is used
+only on an armhf userland with Debian 12 or older. On a 64-bit userland or trixie it is
+compiled on the device from `files/irserver-src.tar.gz` instead (the 2019 sources need
+GCC's newer hard errors downgraded; see `tasks/build.yml`). Automatic; override with
+`pi_irserver_build_from_source: true|false`.
diff --git a/roles/pi_irserver/defaults/main.yml b/roles/pi_irserver/defaults/main.yml
new file mode 100644
index 0000000..a120b81
--- /dev/null
+++ b/roles/pi_irserver/defaults/main.yml
@@ -0,0 +1,6 @@
+---
+# The shipped files/irserver is a 32-bit ARM binary linked against libzip.so.4 (Debian
+# bookworm's libzip4 on armhf). It cannot run on a 64-bit userland, and trixie no longer
+# ships libzip.so.4 at all. "auto" uses it only on armhf + Debian <= 12 and compiles
+# files/irserver-src.tar.gz on the device everywhere else; set true/false to force.
+pi_irserver_build_from_source: auto
diff --git a/roles/pi_irserver/tasks/build.yml b/roles/pi_irserver/tasks/build.yml
new file mode 100644
index 0000000..b6d839e
--- /dev/null
+++ b/roles/pi_irserver/tasks/build.yml
@@ -0,0 +1,44 @@
+---
+- name: Install irserver build dependencies
+  ansible.builtin.apt:
+    name:
+      - build-essential
+      - libzip-dev
+    cache_valid_time: 7200
+
+- name: Create irserver source directory
+  ansible.builtin.file:
+    path: /opt/irserver-src
+    state: directory
+    mode: "0755"
+
+- name: Unpack irserver source
+  ansible.builtin.unarchive:
+    src: irserver-src.tar.gz
+    dest: /opt/irserver-src
+    creates: /opt/irserver-src/makefile
+
+- name: Build irserver
+  # The 2019 sources predate modern C: GCC 14 rejects implicit function declarations,
+  # implicit int and a few pointer/int mix-ups as hard errors. They are old but working
+  # code, so the errors are downgraded rather than the source patched. libzip comes from
+  # libzip-dev (`irserver_arm_noccf` links -lzip); the bundled 32-bit static libzip*.a
+  # are not used. `arm/` is where the makefile puts its objects.
+  ansible.builtin.shell:
+    cmd: |
+      set -e
+      mkdir -p arm
+      make irserver_arm_noccf LDFLAGS="-lzip" \
+        CFLAGS="-w -Wno-error=implicit-function-declaration -Wno-error=int-conversion \
+                -Wno-error=incompatible-pointer-types -Wno-error=return-mismatch \
+                -Wno-error=implicit-int"
+    chdir: /opt/irserver-src
+    creates: /opt/irserver-src/irserver
+
+- name: Install built irserver
+  ansible.builtin.copy:
+    src: /opt/irserver-src/irserver
+    dest: /usr/bin/irserver
+    mode: u+rx
+    remote_src: true
+  notify: Restart irserver
diff --git a/roles/pi_irserver/tasks/main.yml b/roles/pi_irserver/tasks/main.yml
index 81c34e4..dcec9a5 100644
--- a/roles/pi_irserver/tasks/main.yml
+++ b/roles/pi_irserver/tasks/main.yml
@@ -1,10 +1,27 @@
 ---
-- name: Copy irserver
+- name: Get the userland architecture
+  # See pi_squeezelite_custom: the kernel's architecture is not the userland's.
+  ansible.builtin.command: dpkg --print-architecture
+  register: pi_irserver_dpkg_arch
+  changed_when: false
+  check_mode: false # read-only
+- name: Decide between the prebuilt binary and a build on the device
+  ansible.builtin.set_fact:
+    pi_irserver_build: >-
+      {{ (pi_irserver_build_from_source | string | lower == 'true')
+         or (pi_irserver_build_from_source | string | lower == 'auto'
+             and (pi_irserver_dpkg_arch.stdout | trim != 'armhf'
+                  or ansible_facts.distribution_major_version | int >= 13)) }}
+- name: Copy prebuilt irserver (32-bit ARM binary)
   ansible.builtin.copy:
     src: irserver
     dest: /usr/bin/irserver
     mode: u+rx
   notify: Restart irserver
+  when: not pi_irserver_build
+- name: Build irserver from source (needed on a 64-bit userland, see README)
+  ansible.builtin.include_tasks: build.yml
+  when: pi_irserver_build
 - name: Make config dir for remotes
   ansible.builtin.file:
     path: /usr/bin/remotes