diff --git a/modules/pacman/README.md b/modules/pacman/README.md
index ae53b6b8..4ba4969a 100644
--- a/modules/pacman/README.md
+++ b/modules/pacman/README.md
@@ -33,9 +33,13 @@ that seat (ADR 0207).
   - **The outcome is the module's health.** The timer's resource asks `pacman_upgrade_health`: unhealthy,
     naming the exit and the last `error:` line of the journal, when the last weekly upgrade failed; healthy
     while it runs, after it passed, and before it ever ran. The controller raises the module's condition for
-    the node from it. A failed service stays failed until the next run, so the condition stands until an
-    upgrade passes, a hand `pacman_upgrade` does not clear it. A restart of the machine forgets the failed
-    state (the service manager's), so it is the condition raised before it that keeps the record.
+    the node from it. A failed service stays failed until
+    the next run, so the condition stands until an upgrade passes; a hand `pacman_upgrade` does not clear
+    it. A restart of the machine clears the failed state and with it the condition, and the next Saturday
+    runs again. A run that goes on longer than two hours is unhealthy too, naming when it started and the
+    last line of its journal: it is hung and holds pacman's database lock. The service has no start
+    timeout on purpose, because killing pacman in the middle of a transaction is worse; the hung run is
+    said, not killed.
 
 ## What it improves
 
diff --git a/modules/pacman/cmd/pacman-tools/pacman_test.go b/modules/pacman/cmd/pacman-tools/pacman_test.go
index c17b9d48..4ca7f5bb 100644
--- a/modules/pacman/cmd/pacman-tools/pacman_test.go
+++ b/modules/pacman/cmd/pacman-tools/pacman_test.go
@@ -378,8 +378,9 @@ func TestConfigIsReadAsPacmanConfResolvesIt(t *testing.T) {
 // The weekly upgrade's outcome is the module's health (issue 1574, ADR 0477 clause 5).
 func upgradeHealthMachine(props, journal string) *Machine {
 	return machine(byLine(map[string]Ran{
-		"systemctl show " + WeeklyUnit + " --no-pager --property=LoadState --property=ActiveState --property=Result --property=ExecMainStatus --property=ExecMainExitTimestamp": {Stdout: props},
+		"systemctl show " + WeeklyUnit + " --no-pager --property=LoadState --property=ActiveState --property=Result --property=ExecMainStatus --property=ExecMainExitTimestamp --property=ExecMainStartTimestamp": {Stdout: props},
 		"sudo -n journalctl --no-pager -o cat -n 40 -u " + WeeklyUnit: {Stdout: journal},
+		"sudo -n journalctl --no-pager -o cat -n 1 -u " + WeeklyUnit:  {Stdout: journal},
 	}, nil), 1000)
 }
 
@@ -398,7 +399,7 @@ func TestAFailedWeeklyUpgradeIsUnhealthyNamingTheError(t *testing.T) {
 func TestAPassedRunningOrNeverRunWeeklyUpgradeIsHealthy(t *testing.T) {
 	for name, props := range map[string]string{
 		"passed":    "LoadState=loaded\nActiveState=inactive\nResult=success\nExecMainStatus=0\nExecMainExitTimestamp=Sat 2026-10-24 04:09:00 CEST\n",
-		"running":   "LoadState=loaded\nActiveState=activating\nResult=success\nExecMainStatus=0\nExecMainExitTimestamp=\n",
+		"running":   "LoadState=loaded\nActiveState=activating\nResult=success\nExecMainStatus=0\nExecMainExitTimestamp=\nExecMainStartTimestamp=Wed 2026-10-04 11:50:00 UTC\n",
 		"never run": "LoadState=loaded\nActiveState=inactive\nResult=success\nExecMainStatus=0\nExecMainExitTimestamp=\n",
 	} {
 		if h := upgradeHealthMachine(props, "").UpgradeHealth(); !h.Healthy {
@@ -409,3 +410,21 @@ func TestAPassedRunningOrNeverRunWeeklyUpgradeIsHealthy(t *testing.T) {
 		t.Errorf("a unit that cannot be read is not healthy: %+v", h)
 	}
 }
+
+// A run that goes on past RunLimit is hung and holds pacman's lock: unhealthy, naming its start (issue 1574).
+func TestAHungWeeklyUpgradeIsUnhealthyNamingItsStart(t *testing.T) {
+	// the test machine's clock is 2026-10-04 12:00 UTC
+	h := upgradeHealthMachine("LoadState=loaded\nActiveState=activating\nResult=success\nExecMainStatus=0\nExecMainStartTimestamp=Wed 2026-10-04 09:00:00 UTC\n",
+		"downloading linux-6.99...\n").UpgradeHealth()
+	if h.Healthy || !strings.Contains(h.Why, "Wed 2026-10-04 09:00:00 UTC") || !strings.Contains(h.Why, "downloading linux-6.99") {
+		t.Fatalf("started 3 h ago: %+v", h)
+	}
+	h = upgradeHealthMachine("LoadState=loaded\nActiveState=activating\nResult=success\nExecMainStatus=0\nExecMainStartTimestamp=Wed 2026-10-04 11:50:00 UTC\n", "").UpgradeHealth()
+	if !h.Healthy {
+		t.Fatalf("started 10 min ago: %+v", h)
+	}
+	h = upgradeHealthMachine("LoadState=loaded\nActiveState=activating\nResult=success\nExecMainStatus=0\nExecMainStartTimestamp=\n", "").UpgradeHealth()
+	if h.Healthy {
+		t.Fatalf("a start that cannot be read is not healthy: %+v", h)
+	}
+}
diff --git a/modules/pacman/cmd/pacman-tools/upgrade_health.go b/modules/pacman/cmd/pacman-tools/upgrade_health.go
index 2b817bcf..90180130 100644
--- a/modules/pacman/cmd/pacman-tools/upgrade_health.go
+++ b/modules/pacman/cmd/pacman-tools/upgrade_health.go
@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"strings"
+	"time"
 )
 
 // The weekly upgrade's outcome (issue 1574, ADR 0477 clause 5). The mesh runs a full upgrade on every node
@@ -22,11 +23,20 @@ type Health struct {
 // WeeklyUnit is the service the weekly timer starts.
 const WeeklyUnit = "mesh-pacman-weekly-upgrade.service"
 
+// RunLimit is how long a weekly upgrade may go on before it is unhealthy. The service has no start timeout on
+// purpose: killing pacman in the middle of a transaction leaves a half-upgraded machine. A run past the limit
+// is a hung one (a stuck hook, a stalled transaction), which holds pacman's database lock so that no later run
+// can start; it is said, not killed.
+const RunLimit = 2 * time.Hour
+
+// systemdTime is how systemctl shows a timestamp, in the machine's local time.
+const systemdTime = "Mon 2006-01-02 15:04:05 MST"
+
 // UpgradeHealth judges the last weekly upgrade from its service: unhealthy when it failed, naming the exit
 // and the last error the journal holds; healthy while it runs, after it passed, and before it ever ran. A
 // unit that cannot be read is unhealthy: failure is loud.
 func (m *Machine) UpgradeHealth() Health {
-	p, err := m.unitProps(WeeklyUnit, "LoadState", "ActiveState", "Result", "ExecMainStatus", "ExecMainExitTimestamp")
+	p, err := m.unitProps(WeeklyUnit, "LoadState", "ActiveState", "Result", "ExecMainStatus", "ExecMainExitTimestamp", "ExecMainStartTimestamp")
 	if err != nil {
 		return Health{Why: "the weekly upgrade's service could not be read: " + err.Error()}
 	}
@@ -34,7 +44,7 @@ func (m *Machine) UpgradeHealth() Health {
 	case p["LoadState"] == "not-found":
 		return Health{Healthy: true, Why: "the weekly upgrade's service is not placed yet; no upgrade has run"}
 	case p["ActiveState"] == "activating" || p["ActiveState"] == "active":
-		return Health{Healthy: true, Why: "the weekly upgrade is running"}
+		return m.runningHealth(p["ExecMainStartTimestamp"])
 	case p["ActiveState"] != "failed" && p["Result"] == "success":
 		if at := p["ExecMainExitTimestamp"]; at != "" {
 			return Health{Healthy: true, Why: "the last weekly upgrade passed (" + at + ")"}
@@ -53,6 +63,25 @@ func (m *Machine) UpgradeHealth() Health {
 	return Health{Why: why + "; the next upgrade is the next Saturday 04:00, or a hand pacman_upgrade", Found: found}
 }
 
+// runningHealth judges a run in progress: healthy within RunLimit of its start, unhealthy past it, naming the
+// start and the last line the journal holds.
+func (m *Machine) runningHealth(started string) Health {
+	at, err := time.ParseInLocation(systemdTime, started, time.Local)
+	if err != nil {
+		return Health{Why: fmt.Sprintf("the weekly upgrade is running and when it started could not be read (%q)", started)}
+	}
+	if m.Now().Sub(at) <= RunLimit {
+		return Health{Healthy: true, Why: "the weekly upgrade is running, since " + started}
+	}
+	why := fmt.Sprintf("the weekly upgrade has been running since %s, longer than %s: it is hung, and holds pacman's database lock so no later upgrade can start", started, RunLimit)
+	found := []string{}
+	if ls := m.journal(WeeklyUnit, 1); len(ls) > 0 && !strings.HasPrefix(ls[0], "(the journal could not be read") {
+		why += "; its last line: " + strings.TrimSpace(ls[0])
+		found = append(found, strings.TrimSpace(ls[0]))
+	}
+	return Health{Why: why, Found: found}
+}
+
 // lastError is the last line pacman marked as an error, else the last line the journal holds; a journal that
 // could not be read says so in one line starting with "(", which is no error to name.
 func lastError(journal []string) string {