diff --git a/setup/zpush.sh b/setup/zpush.sh
index 33a0a6cf..3d441e8d 100755
--- a/setup/zpush.sh
+++ b/setup/zpush.sh
@@ -55,12 +55,20 @@ if [ $needs_update == 1 ]; then
 fi
 
 # HACK z-push for php 8.0
-# see: https://github.com/mail-in-a-box/mailinabox/pull/2083#issuecomment-1237232402
+# see: https://github.com/mail-in-a-box/mailinabox/issues/2177#issuecomment-1294430425
 if [ "$PHP_VER" = "8.0" ]; then
     # change a z-push source code logging line so it doesn't print the mutexid or memid, which cause an exception ("Uncaught Error: Object of class SysvSemaphore could not be converted to string in /usr/local/lib/z-push/backend/ipcsharedmemory/ipcsharedmemoryprovider.php:45"
     sed -i 's/\(Initialized mutexid\) %s\( and memid\) %s/\1\2/' /usr/local/lib/z-push/backend/ipcsharedmemory/ipcsharedmemoryprovider.php
     # change the default value of maxattsize from '' to -1 in policies.ini
     tools/editconf.py /usr/local/lib/z-push/policies.ini -ini-section default -c ';' maxattsize=-1
+    # change interval->format("%a") to interval->format("%d") in caldav.php
+    xt=$(mktemp)
+    awk 'BEGIN {prev=""} /format\("%a"\)/ && prev ~ /DateInterval/ { gsub(/%a/,"%d") } { prev=$0; print }' /usr/local/lib/z-push/backend/caldav/caldav.php >>$xt
+    if [ $(diff -y --suppress-common-lines "$xt" /usr/local/lib/z-push/backend/caldav/caldav.php | wc -l) -eq 1 ]; then
+        # verified: only 1 line was changed
+        cp "$xt" /usr/local/lib/z-push/backend/caldav/caldav.php
+    fi
+    rm "$xt"
 fi
 
 # Configure default config.