diff --git a/fetch-calendar.sh b/fetch-calendar.sh
index 6586fdb..fac7c5d 100755
--- a/fetch-calendar.sh
+++ b/fetch-calendar.sh
@@ -2,8 +2,23 @@
 set -eu
 
 ICAL_URL=https://cloud.hamburg.ccc.de/remote.php/dav/public-calendars/6CJcM7XDfoYire5d
-START_TIME=$(date -v-1d +%s) # yesterday
-END_TIME=$(date -v+1m +%s) # now + 1 month
 OUTFILE=data/calendar.json
 
+# See here for uname -s outputs: https://en.wikipedia.org/wiki/Uname#Examples
+OS_TYPE=$(uname -s)
+if [ "$OS_TYPE" = "Linux" ]; then
+    START_TIME=$(date --date="-1 day" +%s) # yesterday
+    END_TIME=$(date --date="+1 month" +%s) # now + 1 month
+elif [ "$OS_TYPE" = "Darwin" ] || [ "$OS_TYPE" = "FreeBSD" ]; then
+    START_TIME=$(date -v-1d +%s) # yesterday
+    END_TIME=$(date -v+1m +%s) # now + 1 month
+else
+    echo "ERROR: Unsupported OS type"
+    return 1
+fi
+
+mkdir -p $(dirname $OUTFILE)
+
+echo "loading calendar file..."
 curl -s $ICAL_URL\?export\&accept=jcal\&expand\=1\&start\=$START_TIME\&end\=$END_TIME | jq '.[2]|map({_type:.[0]}+(.[1]|map({key:.[0],value:.[3]})|from_entries))' > $OUTFILE
+echo "...done"