diff --git a/ci/check-warnings b/ci/check-warnings
index cc396423..89ae955d 100755
--- a/ci/check-warnings
+++ b/ci/check-warnings
@@ -7,7 +7,8 @@ set -e -u
 
 LOGFILE=$1
 
-if test -s $LOGFILE; then
+LINES=$(grep --invert-match "attempting MIRRORS if available" $LOGFILE | wc -l)
+if test "$LINES" -ne 0; then
     echo ==============================
     echo The build had warnings/errors:
     echo ==============================