diff --git a/PVE/API2/Qemu.pm b/PVE/API2/Qemu.pm
index feb9ea8b..5015d82c 100644
--- a/PVE/API2/Qemu.pm
+++ b/PVE/API2/Qemu.pm
@@ -670,6 +670,20 @@ __PACKAGE__->register_method({
 			$conf->{vmgenid} = PVE::QemuServer::generate_uuid();
 		    }
 
+		    my $machine = $conf->{machine};
+		    if (!$machine || $machine =~ m/^(?:pc|q35|virt)$/) {
+			# always pin Windows' machine version on create, they get to easily confused
+			if (PVE::QemuServer::windows_version($conf->{ostype})) {
+			    my $pin_version = PVE::QemuServer::kvm_user_version();
+			    if (!$machine || $machine eq 'pc') {
+				$machine = "pc-i440fx-$pin_version";
+			    } elsif ($machine eq 'q35') {
+				$machine = "pc-q35-$pin_version";
+			    }
+			    $conf->{machine} = $machine;
+			}
+		    }
+
 		    PVE::QemuConfig->write_config($vmid, $conf);
 
 		};
diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
index 2ee79339..0ac4fcfe 100644
--- a/PVE/QemuServer.pm
+++ b/PVE/QemuServer.pm
@@ -2897,10 +2897,25 @@ sub get_vm_machine {
     my $machine = $forcemachine || $conf->{machine};
 
     if (!$machine || $machine =~ m/^(?:pc|q35|virt)$/) {
+	$kvmversion //= kvm_user_version();
+	# we must pin Windows VMs without a specific version to 5.1, as 5.2 fixed a bug in ACPI
+	# layout which confuses windows quite a bit and may result in various regressions..
+	# see: https://lists.gnu.org/archive/html/qemu-devel/2021-02/msg08484.html
+	if (windows_version($conf->{ostype})) {
+	    my $pin_version = '5.1';
+	    if (!PVE::QemuServer::Machine::can_run_pve_machine_version($pin_version, $kvmversion)) {
+		$kvmversion =~ m/^(\d+\.\d+)/;
+		$pin_version = $1;
+	    }
+	    if (!$machine || $machine eq 'pc') {
+		$machine = "pc-i440fx-$pin_version";
+	    } elsif ($machine eq 'q35') {
+		$machine = "pc-q35-$pin_version";
+	    }
+	}
 	$arch //= 'x86_64';
 	$machine ||= $default_machines->{$arch};
 	if ($add_pve_version) {
-	    $kvmversion //= kvm_user_version();
 	    my $pvever = PVE::QemuServer::Machine::get_pve_version($kvmversion);
 	    $machine .= "+pve$pvever";
 	}
diff --git a/test/cfg2cmd/custom-cpu-model-host-phys-bits.conf.cmd b/test/cfg2cmd/custom-cpu-model-host-phys-bits.conf.cmd
index ea5dfc85..5492477c 100644
--- a/test/cfg2cmd/custom-cpu-model-host-phys-bits.conf.cmd
+++ b/test/cfg2cmd/custom-cpu-model-host-phys-bits.conf.cmd
@@ -24,5 +24,5 @@
   -device 'virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3' \
   -iscsi 'initiator-name=iqn.1993-08.org.debian:01:aabbccddeeff' \
   -rtc 'driftfix=slew,base=localtime' \
-  -machine 'type=pc+pve0' \
+  -machine 'type=pc-i440fx-5.1+pve0' \
   -global 'kvm-pit.lost_tick_policy=discard'
diff --git a/test/cfg2cmd/custom-cpu-model.conf.cmd b/test/cfg2cmd/custom-cpu-model.conf.cmd
index 7ad2e9b9..af27b65e 100644
--- a/test/cfg2cmd/custom-cpu-model.conf.cmd
+++ b/test/cfg2cmd/custom-cpu-model.conf.cmd
@@ -24,5 +24,5 @@
   -device 'virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3' \
   -iscsi 'initiator-name=iqn.1993-08.org.debian:01:aabbccddeeff' \
   -rtc 'driftfix=slew,base=localtime' \
-  -machine 'type=pc+pve0' \
+  -machine 'type=pc-i440fx-5.1+pve0' \
   -global 'kvm-pit.lost_tick_policy=discard'
diff --git a/test/cfg2cmd/i440fx-win10-hostpci.conf.cmd b/test/cfg2cmd/i440fx-win10-hostpci.conf.cmd
index a9c27209..f926be00 100644
--- a/test/cfg2cmd/i440fx-win10-hostpci.conf.cmd
+++ b/test/cfg2cmd/i440fx-win10-hostpci.conf.cmd
@@ -34,5 +34,5 @@
   -netdev 'type=tap,id=net0,ifname=tap8006i0,script=/var/lib/qemu-server/pve-bridge,downscript=/var/lib/qemu-server/pve-bridgedown,vhost=on' \
   -device 'virtio-net-pci,mac=2E:01:68:F9:9C:87,netdev=net0,bus=pci.0,addr=0x12,id=net0,bootindex=300' \
   -rtc 'driftfix=slew,base=localtime' \
-  -machine 'type=pc+pve0' \
+  -machine 'type=pc-i440fx-5.1+pve0' \
   -global 'kvm-pit.lost_tick_policy=discard'
diff --git a/test/cfg2cmd/q35-win10-hostpci.conf.cmd b/test/cfg2cmd/q35-win10-hostpci.conf.cmd
index 4572348f..0ad8a3e0 100644
--- a/test/cfg2cmd/q35-win10-hostpci.conf.cmd
+++ b/test/cfg2cmd/q35-win10-hostpci.conf.cmd
@@ -35,5 +35,5 @@
   -netdev 'type=tap,id=net0,ifname=tap8006i0,script=/var/lib/qemu-server/pve-bridge,downscript=/var/lib/qemu-server/pve-bridgedown,vhost=on' \
   -device 'virtio-net-pci,mac=2E:01:68:F9:9C:87,netdev=net0,bus=pci.0,addr=0x12,id=net0,bootindex=300' \
   -rtc 'driftfix=slew,base=localtime' \
-  -machine 'type=q35+pve0' \
+  -machine 'type=pc-q35-5.1+pve0' \
   -global 'kvm-pit.lost_tick_policy=discard'
diff --git a/test/cfg2cmd/spice-win.conf.cmd b/test/cfg2cmd/spice-win.conf.cmd
index 78e3c5e5..47dbd707 100644
--- a/test/cfg2cmd/spice-win.conf.cmd
+++ b/test/cfg2cmd/spice-win.conf.cmd
@@ -34,5 +34,5 @@
   -netdev 'type=tap,id=net0,ifname=tap8006i0,script=/var/lib/qemu-server/pve-bridge,downscript=/var/lib/qemu-server/pve-bridgedown,vhost=on' \
   -device 'virtio-net-pci,mac=A2:C0:43:77:08:A1,netdev=net0,bus=pci.0,addr=0x12,id=net0,bootindex=300' \
   -rtc 'driftfix=slew,base=localtime' \
-  -machine 'type=pc' \
+  -machine 'type=pc-i440fx-4.0' \
   -global 'kvm-pit.lost_tick_policy=discard'