diff --git a/src/ci/scripts/free-disk-space.sh b/src/ci/scripts/free-disk-space.sh
index 706ccaeb67f4e..50be23602fa5e 100755
--- a/src/ci/scripts/free-disk-space.sh
+++ b/src/ci/scripts/free-disk-space.sh
@@ -23,11 +23,10 @@ printSeparationLine() {
 # macro to compute available space
 # REF: https://unix.stackexchange.com/a/42049/60849
 # REF: https://stackoverflow.com/a/450821/408734
-getAvailableSpace() { df -a "$1" | awk 'NR > 1 {avail+=$4} END {print avail}'; }
-
+getAvailableSpace() { echo $(df -a $1 | awk 'NR > 1 {avail+=$4} END {print avail}'); }
 # macro to make Kb human readable (assume the input is Kb)
 # REF: https://unix.stackexchange.com/a/44087/60849
-formatByteCount() { numfmt --to=iec-i --suffix=B --padding=7 "$1"'000'; }
+formatByteCount() { echo $(numfmt --to=iec-i --suffix=B --padding=7 $1'000'); }
 
 # macro to output saved space
 printSavedSpace() {