diff --git a/tools/rapport_activite.sh b/tools/rapport_activite.sh
index c2282ad5..5073b1bc 100755
--- a/tools/rapport_activite.sh
+++ b/tools/rapport_activite.sh
@@ -83,7 +83,7 @@ if [ "$#" = 1 ] && [ "$1" = "-h" ]; then
     help
 elif [ "$#" = 1 ] && [ "$1" = "-p" ]; then
     if [ "$(date +%m)" -gt 1 ]; then
-	precedingMonth="$(($(date +%m)-1))"
+	precedingMonth="$((10#$(date +%m)-1))"
 	year="$(date +%Y)"
 	if [ $precedingMonth -lt 10 ]; then
 	    yearMonth="$year-0$precedingMonth"