diff --git a/contrib/purge_api/purge_history.sh b/contrib/purge_api/purge_history.sh
index 9d5324ea1c..de58dcdbb7 100644
--- a/contrib/purge_api/purge_history.sh
+++ b/contrib/purge_api/purge_history.sh
@@ -84,7 +84,9 @@ AUTH="Authorization: Bearer $TOKEN"
 ###################################################################################################
 # finally start pruning the room:
 ###################################################################################################
-POSTDATA='{"delete_local_events":"true"}' # this will really delete local events, so the messages in the room really disappear unless they are restored by remote federation
+# this will really delete local events, so the messages in the room really
+# disappear unless they are restored by remote federation. This is because
+# we pass {"delete_local_events":true} to the curl invocation below.
 
 for ROOM in "${ROOMS_ARRAY[@]}"; do
     echo "########################################### $(date) ################# "
@@ -104,7 +106,7 @@ for ROOM in "${ROOMS_ARRAY[@]}"; do
       SLEEP=2
       set -x
       # call purge
-      OUT=$(curl --header "$AUTH" -s -d $POSTDATA POST "$API_URL/admin/purge_history/$ROOM/$EVENT_ID")
+      OUT=$(curl --header "$AUTH" -s -d '{"delete_local_events":true}' POST "$API_URL/admin/purge_history/$ROOM/$EVENT_ID")
       PURGE_ID=$(echo "$OUT" |grep purge_id|cut -d'"' -f4 )
       if [ "$PURGE_ID" == "" ]; then
         # probably the history purge is already in progress for $ROOM