diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index 6a524dfdb9511890b95e742c55cf034f2fc6031a..16f7eae253d4f3b5e4c106c226c22977d3e2d557 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -3283,7 +3283,14 @@
           </dd>
           <dt>scsi</dt>
           <dd>SCSI devices are described by both the <code>adapter</code>
-            and <code>address</code> elements.
+            and <code>address</code> elements. The <code>address</code>
+            element includes a <code>bus</code> attribute (a 2-digit bus
+            number), a <code>target</code> attribute (a 10-digit target
+            number), and a <code>unit</code> attribute (a 20-digit unit
+            number on the bus). Not all hypervisors support larger
+            <code>target</code> and <code>unit</code> values. It is up
+            to each hypervisor to determine the maximum value supported
+            for the adapter.
             <p>
             <span class="since">Since 1.2.8</span>, the <code>source</code>
             element of a SCSI device may contain the <code>protocol</code>
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index ca3bcfcb8d94d0978ff2cca355f8d30f0d43102e..3014365bb5bd08639b48d993b1b1a0fff0110296 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -3833,10 +3833,10 @@
       <ref name="driveBus"/>
     </attribute>
     <attribute name="target">
-      <ref name="driveTarget"/>
+      <ref name="driveSCSITarget"/>
     </attribute>
     <attribute name="unit">
-      <ref name="driveUnit"/>
+      <ref name="driveSCSIUnit"/>
     </attribute>
   </define>
   <define name="usbportaddress">
@@ -5152,11 +5152,21 @@
       <param name="pattern">[0-9]{1,2}</param>
     </data>
   </define>
+  <define name="driveSCSITarget">
+    <data type="string">
+      <param name="pattern">[0-9]{1,10}</param>
+    </data>
+  </define>
   <define name="driveUnit">
     <data type="string">
       <param name="pattern">[0-9]{1,2}</param>
     </data>
   </define>
+  <define name="driveSCSIUnit">
+    <data type="string">
+      <param name="pattern">[0-9]{1,20}</param>
+    </data>
+  </define>
   <define name="featureName">
     <data type="string">
       <param name='pattern'>[a-zA-Z0-9\-_\.]+</param>
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-hostdev-scsi-large-unit.xml b/tests/qemuxml2argvdata/qemuxml2argv-hostdev-scsi-large-unit.xml
new file mode 100644
index 0000000000000000000000000000000000000000..b5efb408eeaf4f66b238b62bec51c50abdef5fe8
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-hostdev-scsi-large-unit.xml
@@ -0,0 +1,35 @@
+<domain type='qemu'>
+  <name>QEMUGuest2</name>
+  <uuid>c7a5fdbd-edaf-9466-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>219100</memory>
+  <currentMemory unit='KiB'>219100</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu</emulator>
+    <disk type='block' device='disk'>
+      <source dev='/dev/HostVG/QEMUGuest2'/>
+      <target dev='hda' bus='ide'/>
+      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
+    </disk>
+    <controller type='scsi' index='0' model='virtio-scsi'/>
+    <controller type='usb' index='0'/>
+    <controller type='ide' index='0'/>
+    <controller type='pci' index='0' model='pci-root'/>
+    <hostdev mode='subsystem' type='scsi' managed='yes'>
+      <source>
+        <adapter name='scsi_host0'/>
+        <address bus='0' target='0' unit='1074872354'/>
+      </source>
+      <address type='drive' controller='0' bus='0' target='4' unit='8'/>
+    </hostdev>
+    <memballoon model='virtio'/>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2xmltest.c b/tests/qemuxml2xmltest.c
index 3287ea37d5f4ea0ecc9e4162ea6a155ec248fe1a..711827dfe66d8e757bd66c77de652a5c6e3b86b8 100644
--- a/tests/qemuxml2xmltest.c
+++ b/tests/qemuxml2xmltest.c
@@ -577,6 +577,7 @@ mymain(void)
     DO_TEST("hostdev-scsi-rawio");
 
     DO_TEST_DIFFERENT("hostdev-scsi-autogen-address");
+    DO_TEST("hostdev-scsi-large-unit");
 
     DO_TEST("hostdev-scsi-lsi-iscsi");
     DO_TEST("hostdev-scsi-lsi-iscsi-auth");