diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
index 430661a7..aff33728 100644
--- a/PVE/QemuServer.pm
+++ b/PVE/QemuServer.pm
@@ -1521,6 +1521,17 @@ sub print_drivedevice_full {
 	my $maxdev = ($drive->{interface} eq 'sata') ? $PVE::QemuServer::Drive::MAX_SATA_DISKS : 2;
 	my $controller = int($drive->{index} / $maxdev);
 	my $unit = $drive->{index} % $maxdev;
+
+	# machine type q35 only supports unit=0 for IDE rather than 2 units. This wasn't handled
+	# correctly before, so e.g. index=2 was mapped to controller=1,unit=0 rather than
+	# controller=2,unit=0. Note that odd indices never worked, as they would be mapped to
+	# unit=1, so to keep backwards compat for migration, it suffices to keep even ones as they
+	# were before. Move odd ones up by 2 where they don't clash.
+	if (PVE::QemuServer::Machine::machine_type_is_q35($conf) && $drive->{interface} eq 'ide') {
+	    $controller += 2 * ($unit % 2);
+	    $unit = 0;
+	}
+
 	my $devicetype = ($drive->{media} && $drive->{media} eq 'cdrom') ? "cd" : "hd";
 
 	$device = "ide-$devicetype";
diff --git a/test/cfg2cmd/q35-ide.conf.cmd b/test/cfg2cmd/q35-ide.conf.cmd
index 7755fdb0..f23d90f3 100644
--- a/test/cfg2cmd/q35-ide.conf.cmd
+++ b/test/cfg2cmd/q35-ide.conf.cmd
@@ -25,11 +25,11 @@
   -drive 'file=/mnt/pve/cifs-store/template/iso/zero.iso,if=none,id=drive-ide0,media=cdrom,aio=threads' \
   -device 'ide-cd,bus=ide.0,unit=0,drive=drive-ide0,id=ide0,bootindex=200' \
   -drive 'file=/mnt/pve/cifs-store/template/iso/one.iso,if=none,id=drive-ide1,media=cdrom,aio=threads' \
-  -device 'ide-cd,bus=ide.0,unit=1,drive=drive-ide1,id=ide1,bootindex=201' \
+  -device 'ide-cd,bus=ide.2,unit=0,drive=drive-ide1,id=ide1,bootindex=201' \
   -drive 'file=/mnt/pve/cifs-store/template/iso/two.iso,if=none,id=drive-ide2,media=cdrom,aio=threads' \
   -device 'ide-cd,bus=ide.1,unit=0,drive=drive-ide2,id=ide2,bootindex=202' \
   -drive 'file=/mnt/pve/cifs-store/template/iso/three.iso,if=none,id=drive-ide3,media=cdrom,aio=threads' \
-  -device 'ide-cd,bus=ide.1,unit=1,drive=drive-ide3,id=ide3,bootindex=203' \
+  -device 'ide-cd,bus=ide.3,unit=0,drive=drive-ide3,id=ide3,bootindex=203' \
   -device 'virtio-scsi-pci,id=scsihw0,bus=pci.0,addr=0x5' \
   -drive 'file=/var/lib/vz/images/100/vm-100-disk-2.qcow2,if=none,id=drive-scsi0,format=qcow2,cache=none,aio=io_uring,detect-zeroes=on' \
   -device 'scsi-hd,bus=scsihw0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0,bootindex=100' \