diff --git a/data/usr/lib/systemd/system/freedombox-privileged.service b/data/usr/lib/systemd/system/freedombox-privileged.service
index 68aaebda8..fc0827ce7 100644
--- a/data/usr/lib/systemd/system/freedombox-privileged.service
+++ b/data/usr/lib/systemd/system/freedombox-privileged.service
@@ -7,6 +7,8 @@ Documentation=https://wiki.debian.org/FreedomBox/
 StartLimitIntervalSec=0
 # Stop/restart along with .socket unit (invoked from dpkg scripts).
 PartOf=freedombox-privileged.socket
+# Uploaded files in /var/tmp/ are shared with FreedomBox web service.
+JoinsNamespaceOf=plinth.service
 
 [Service]
 Type=notify
@@ -15,8 +17,9 @@ TimeoutSec=300s
 User=root
 Group=root
 NotifyAccess=main
-# Uploaded files in /var/tmp/ are shared with FreedomBox web service.
-#PrivateTmp=yes
+# Uploaded files in /var/tmp/ are shared with FreedomBox web service by joining
+# namespaces.
+PrivateTmp=yes
 Restart=on-failure
 # Don't restart too fast
 RestartSec=1
diff --git a/data/usr/lib/systemd/system/plinth.service b/data/usr/lib/systemd/system/plinth.service
index 2341b2745..85a6abda7 100644
--- a/data/usr/lib/systemd/system/plinth.service
+++ b/data/usr/lib/systemd/system/plinth.service
@@ -5,6 +5,8 @@ Description=FreedomBox Service (Plinth)
 Documentation=man:plinth(1)
 After=network.target
 StartLimitIntervalSec=0
+# Uploaded files in /var/tmp/ are shared with FreedomBox privileged service.
+JoinsNamespaceOf=freedombox-privileged.service
 
 [Service]
 Type=notify
@@ -18,6 +20,8 @@ Group=plinth
 StandardOutput=null
 StandardError=null
 NotifyAccess=main
+# Uploaded files in /var/tmp/ are shared with FreedomBox privileged service by
+# joining namespaces.
 PrivateTmp=yes
 
 [Install]