diff --git a/internal/proxmox/query.go b/internal/proxmox/query.go
index 43bfa72..0286893 100644
--- a/internal/proxmox/query.go
+++ b/internal/proxmox/query.go
@@ -63,13 +63,16 @@ func (c *Client) ListSnapshots(ctx context.Context, vmid int) ([]Snapshot, error
 	return ss, c.get(ctx, path, &ss)
 }
 
-// ListRunningTasks returns the node's currently-running tasks (GET /nodes/{node}/tasks?running=1).
+// ListRunningTasks returns the node's currently-active tasks (GET /nodes/{node}/tasks?source=active).
 // The startup stale-lock recovery uses it as the load-bearing safety guard: a backup lock is cleared
 // ONLY when no vzdump task is genuinely in-flight for the guest (an agent restart while a real backup
-// runs must never clear the live lock).
+// runs must never clear the live lock). NOTE: PVE 9.x rejects `?running=1` ("property not defined in
+// schema") — `source=active` is the supported filter (it returns the RUNNING tasks); confirmed live on
+// felhom-pve (PVE 9.2.2). active-source entries carry status "RUNNING"; we match on type+id, so the
+// case difference vs the by-UPID status endpoint ("running") is moot.
 func (c *Client) ListRunningTasks(ctx context.Context) ([]TaskStatus, error) {
 	var ts []TaskStatus
-	return ts, c.get(ctx, "/nodes/"+c.node+"/tasks?running=1", &ts)
+	return ts, c.get(ctx, "/nodes/"+c.node+"/tasks?source=active", &ts)
 }
 
 // ListStorage returns GET /storage (cluster-wide storage definitions).