diff --git a/admin-system/wan-monitor.yaml b/admin-system/wan-monitor.yaml
index 092566e..9fb0082 100644
--- a/admin-system/wan-monitor.yaml
+++ b/admin-system/wan-monitor.yaml
@@ -146,12 +146,13 @@ data:
       mv "$SHARED/.metrics.tmp" "$SHARED/metrics"
     }
 
-    run_irtt() {  # $1 condition  $2 outfile  $3 duration(seconds)
+    run_irtt() {
       timeout "$(( $3 + 25 ))" irtt client -i "$IRTT_INTERVAL" -d "${3}s" -q $HMAC_OPT \
         -o - "${HETZNER}:${IRTT_PORT}" 2>/dev/null \
-        | python3 /scripts/irtt_to_prom.py "$1" "$IRTT_TARGET" > "$2"
+        | python3 /scripts/irtt_to_prom.py "$1" "$IRTT_TARGET" > "$2.tmp"
+      mv "$2.tmp" "$2"
     }
-
+    
     run_tput() {
       P="${IPERF_PARALLEL:-4}"   # parallel streams: a single stream can't fill 1 Gbps over the RTT
       TO="$(( TPUT_TIME + 20 ))"