diff --git a/install/hardware/fix-synaptic-touchpad.sh b/install/hardware/fix-synaptic-touchpad.sh
index d30dd271..00b3396c 100644
--- a/install/hardware/fix-synaptic-touchpad.sh
+++ b/install/hardware/fix-synaptic-touchpad.sh
@@ -1,6 +1,25 @@
 # Enable Synaptics InterTouch for confirmed touchpads if not already loaded
-
-if grep -qi synaptics /proc/bus/input/devices \
-   && ! lsmod | grep -q '^psmouse'; then
-  modprobe psmouse synaptics_intertouch=1
+#
+# Only when modprobe can resolve psmouse for the running kernel, and never
+# fatally. Installs run this under arch-chroot, where uname -r still names the
+# live ISO's kernel while /lib/modules holds the target's -- the two differ on
+# every machine that is not a T2 Mac, so modprobe failed with "Module psmouse
+# not found in directory /lib/modules/<live kernel>" and took the whole install
+# down with it. Asking modprobe itself first (-qn resolves a module without
+# loading it) keeps that mismatch quiet, and the warning below covers every
+# other reason it declines. An optional touchpad improvement must not be able to
+# halt an install.
+#
+# Loading a module into the live kernel does nothing for the installed system
+# either way, so this only takes effect when it runs on the booted machine.
+# Persisting the switch instead would mean writing options psmouse
+# synaptics_intertouch=1 to /etc/modprobe.d, which forces the SMBus transport
+# past the kernel's own allowlist on every touchpad merely named "synaptics" in
+# /proc/bus/input/devices -- a wider change than this one, and not one to make
+# blind.
+if grep -qi synaptics "${OMARCHY_SYNAPTIC_INPUT_DEVICES:-/proc/bus/input/devices}" \
+   && ! lsmod | grep -q '^psmouse' \
+   && modprobe -qn psmouse; then
+  modprobe psmouse synaptics_intertouch=1 ||
+    echo "Warning: could not enable Synaptics InterTouch on psmouse" >&2
 fi
diff --git a/test/shell.d/synaptic-touchpad-test.sh b/test/shell.d/synaptic-touchpad-test.sh
new file mode 100755
index 00000000..df4828e6
--- /dev/null
+++ b/test/shell.d/synaptic-touchpad-test.sh
@@ -0,0 +1,82 @@
+#!/bin/bash
+
+set -euo pipefail
+
+source "$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)/base-test.sh"
+
+leaf="$ROOT/install/hardware/fix-synaptic-touchpad.sh"
+all="$ROOT/install/hardware/all.sh"
+
+grep -q 'run_logged .*hardware/fix-synaptic-touchpad.sh' "$all" ||
+  fail "the synaptic touchpad quirk runs during hardware setup"
+pass "the synaptic touchpad quirk runs during hardware setup"
+
+test_tmp=$(mktemp -d)
+trap 'rm -rf "$test_tmp"' EXIT
+
+mkdir -p "$test_tmp/bin"
+modprobe_log="$test_tmp/modprobe.log"
+
+# Only a real load is logged, so a case that expects nothing to happen can say
+# so with an empty log even though the leaf always asks modprobe first whether
+# psmouse resolves against the running kernel.
+cat >"$test_tmp/bin/modprobe" <<'SH'
+#!/bin/bash
+
+if [[ $1 == "-qn" ]]; then
+  exit "${TEST_MODPROBE_RESOLVES:-0}"
+fi
+
+printf '%s\n' "$*" >>"$MODPROBE_LOG"
+exit "${TEST_MODPROBE_STATUS:-0}"
+SH
+
+cat >"$test_tmp/bin/lsmod" <<'SH'
+#!/bin/bash
+
+printf '%s\n' 'Module                  Size  Used by'
+printf '%s\n' "${TEST_LOADED_MODULES:-}"
+SH
+
+chmod +x "$test_tmp/bin"/*
+
+printf '%s\n' 'N: Name="SynPS/2 Synaptics TouchPad"' >"$test_tmp/devices"
+
+# Sourced under errexit the way run_logged runs it, so a failing modprobe would
+# fail the run rather than be swallowed here.
+run_fix() {
+  : >"$modprobe_log"
+
+  MODPROBE_LOG="$modprobe_log" \
+    PATH="$test_tmp/bin:$PATH" \
+    OMARCHY_SYNAPTIC_INPUT_DEVICES="$test_tmp/devices" \
+    TEST_LOADED_MODULES="${1:-}" \
+    TEST_MODPROBE_STATUS="${2:-0}" \
+    TEST_MODPROBE_RESOLVES="${3:-0}" \
+    bash -eE -c 'source "$1"' bash "$leaf"
+}
+
+run_fix
+grep -q 'psmouse synaptics_intertouch=1' "$modprobe_log" ||
+  fail "the synaptic touchpad quirk enables InterTouch on a booted machine"
+pass "the synaptic touchpad quirk enables InterTouch on a booted machine"
+
+# The install-breaking case: under arch-chroot the live kernel's modules are not
+# the ones on disk, so psmouse does not resolve and there is nothing to load.
+run_fix "" 0 1
+if [[ -s $modprobe_log ]]; then
+  fail "the synaptic touchpad quirk skips a kernel that cannot resolve psmouse"
+fi
+pass "the synaptic touchpad quirk skips a kernel that cannot resolve psmouse"
+
+run_fix psmouse
+if [[ -s $modprobe_log ]]; then
+  fail "the synaptic touchpad quirk leaves an already-loaded psmouse alone"
+fi
+pass "the synaptic touchpad quirk leaves an already-loaded psmouse alone"
+
+# An optional touchpad improvement never gets to halt an install, whatever the
+# reason the module declines to load.
+run_fix "" 1 2>/dev/null ||
+  fail "the synaptic touchpad quirk survives a failing modprobe"
+pass "the synaptic touchpad quirk survives a failing modprobe"