diff --git a/server/internal/services/metricrules.go b/server/internal/services/metricrules.go
index 14aff7c..e8f70a3 100644
--- a/server/internal/services/metricrules.go
+++ b/server/internal/services/metricrules.go
@@ -109,7 +109,7 @@ func evalDisk(t models.MonitorTarget, parts []models.Partition) (bool, float64,
 	var worstVal float64
 	var worstMsg string
 	for _, p := range parts {
-		if p.TotalBytes == 0 || (t.Mount != "" && p.Mountpoint != t.Mount) {
+		if p.TotalBytes == 0 || p.UsedBytes > p.TotalBytes || (t.Mount != "" && p.Mountpoint != t.Mount) {
 			continue
 		}
 		var breach bool
diff --git a/server/internal/services/metricrules_test.go b/server/internal/services/metricrules_test.go
index f62ad7b..af37d89 100644
--- a/server/internal/services/metricrules_test.go
+++ b/server/internal/services/metricrules_test.go
@@ -44,6 +44,7 @@ func TestEvaluateMetric(t *testing.T) {
 		{"disk pct missing mount skips", models.MonitorTarget{Metric: MetricDiskPct, Threshold: 90, Mount: "/data"}, srvWith(disk), nil, false, false, ""},
 		{"disk free gb breaches", models.MonitorTarget{Metric: MetricDiskFreeGB, Threshold: 10}, srvWith(disk), nil, true, true, "GB free"},
 		{"zero total partition ignored", models.MonitorTarget{Metric: MetricDiskPct, Threshold: 1}, srvWith(models.Inventory{Partitions: []models.Partition{{Mountpoint: "/proc"}}}), nil, false, false, ""},
+		{"used over total partition ignored", models.MonitorTarget{Metric: MetricDiskFreeGB, Threshold: 10}, srvWith(models.Inventory{Partitions: []models.Partition{{Mountpoint: "/", TotalBytes: 100e9, UsedBytes: 150e9}}}), nil, false, false, ""},
 		{"mem pct", models.MonitorTarget{Metric: MetricMemPct, Threshold: 80}, srvWith(models.Inventory{Memory: models.MemInfo{TotalBytes: 100, UsedBytes: 85}}), nil, true, true, "memory"},
 		{"load per core", models.MonitorTarget{Metric: MetricLoadPerCore, Threshold: 1.5}, srvWith(models.Inventory{CPU: models.CPUInfo{Cores: 4, Load1: 8}}), nil, true, true, "load"},
 		{"load no cores skips", models.MonitorTarget{Metric: MetricLoadPerCore, Threshold: 1.5}, srvWith(models.Inventory{CPU: models.CPUInfo{Load1: 8}}), nil, false, false, ""},