diff --git a/backends/meson.build b/backends/meson.build
index 248ce49..6dee4e9 100644
--- a/backends/meson.build
+++ b/backends/meson.build
@@ -10,8 +10,10 @@
   'confidential-guest-support.c',
 ), numa])
 
-system_ss.add(when: 'CONFIG_POSIX', if_true: files('rng-random.c'))
-system_ss.add(when: 'CONFIG_POSIX', if_true: files('hostmem-file.c'))
+if targetos != 'windows'
+  system_ss.add(files('rng-random.c'))
+  system_ss.add(files('hostmem-file.c'))
+endif
 if targetos == 'linux'
   system_ss.add(files('hostmem-memfd.c'))
 endif
diff --git a/block/meson.build b/block/meson.build
index 7faed96..ddea1e4 100644
--- a/block/meson.build
+++ b/block/meson.build
@@ -88,8 +88,11 @@
   block_ss.add(files('parallels.c', 'parallels-ext.c'))
 endif
 
-block_ss.add(when: 'CONFIG_WIN32', if_true: files('file-win32.c', 'win32-aio.c'))
-block_ss.add(when: 'CONFIG_POSIX', if_true: [files('file-posix.c'), coref, iokit])
+if targetos == 'windows'
+  block_ss.add(files('file-win32.c', 'win32-aio.c'))
+else
+  block_ss.add(files('file-posix.c'), coref, iokit)
+endif
 block_ss.add(when: libiscsi, if_true: files('iscsi-opts.c'))
 if targetos == 'linux'
   block_ss.add(files('nvme.c'))
diff --git a/chardev/meson.build b/chardev/meson.build
index 6d56ad3..9564ace 100644
--- a/chardev/meson.build
+++ b/chardev/meson.build
@@ -12,20 +12,22 @@
   'char-udp.c',
   'char.c',
 ))
-chardev_ss.add(when: 'CONFIG_POSIX', if_true: [files(
-  'char-fd.c',
-  'char-pty.c',
-), util])
-if targetos in ['linux', 'gnu/kfreebsd', 'freebsd', 'dragonfly']
-  chardev_ss.add(files('char-parallel.c'))
+if targetos == 'windows'
+  chardev_ss.add(files(
+    'char-console.c',
+    'char-win-stdio.c',
+    'char-win.c',
+  ))
+else
+  chardev_ss.add(files(
+      'char-fd.c',
+      'char-pty.c',
+    ), util)
+  if targetos in ['linux', 'gnu/kfreebsd', 'freebsd', 'dragonfly']
+    chardev_ss.add(files('char-parallel.c'))
+  endif
 endif
 
-chardev_ss.add(when: 'CONFIG_WIN32', if_true: files(
-  'char-console.c',
-  'char-win-stdio.c',
-  'char-win.c',
-))
-
 chardev_ss = chardev_ss.apply(config_targetos, strict: false)
 
 system_ss.add(files(
diff --git a/hw/usb/meson.build b/hw/usb/meson.build
index 4b44db3..b7755b6 100644
--- a/hw/usb/meson.build
+++ b/hw/usb/meson.build
@@ -44,7 +44,9 @@
 system_ss.add(when: 'CONFIG_USB_AUDIO', if_true: files('dev-audio.c'))
 system_ss.add(when: 'CONFIG_USB_SERIAL', if_true: files('dev-serial.c'))
 system_ss.add(when: 'CONFIG_USB_NETWORK', if_true: files('dev-network.c'))
-system_ss.add(when: ['CONFIG_POSIX', 'CONFIG_USB_STORAGE_MTP'], if_true: files('dev-mtp.c'))
+if targetos != 'windows'
+  system_ss.add(when: 'CONFIG_USB_STORAGE_MTP', if_true: files('dev-mtp.c'))
+endif
 
 # smartcard
 system_ss.add(when: 'CONFIG_USB_SMARTCARD', if_true: files('dev-smartcard-reader.c'))
diff --git a/meson.build b/meson.build
index cf224e2..e37ab28 100644
--- a/meson.build
+++ b/meson.build
@@ -2885,9 +2885,7 @@
 ########################
 
 minikconf = find_program('scripts/minikconf.py')
-config_targetos = {
-  (targetos == 'windows' ? 'CONFIG_WIN32' : 'CONFIG_POSIX'): 'y'
-}
+config_targetos = {}
 
 config_all = {}
 config_all_devices = {}
@@ -3480,8 +3478,11 @@
 
   # os-posix.c contains POSIX-specific functions used by qemu-storage-daemon,
   # os-win32.c does not
-  blockdev_ss.add(when: 'CONFIG_POSIX', if_true: files('os-posix.c'))
-  system_ss.add(when: 'CONFIG_WIN32', if_true: [files('os-win32.c')])
+  if targetos == 'windows'
+    system_ss.add(files('os-win32.c'))
+  else
+    blockdev_ss.add(files('os-posix.c'))
+  endif
 endif
 
 common_ss.add(files('cpu-common.c'))
diff --git a/qga/meson.build b/qga/meson.build
index 50edaf1..1113e7c 100644
--- a/qga/meson.build
+++ b/qga/meson.build
@@ -67,22 +67,25 @@
   'main.c',
   'cutils.c',
 ))
-qga_ss.add(when: 'CONFIG_POSIX', if_true: files(
-  'channel-posix.c',
-  'commands-posix.c',
-  'commands-posix-ssh.c',
-))
-if targetos == 'linux'
-  qga_ss.add(files('commands-linux.c'))
-elif targetos in bsd_oses
-  qga_ss.add(files('commands-bsd.c'))
+if targetos == 'windows'
+  qga_ss.add(files(
+    'channel-win32.c',
+    'commands-win32.c',
+    'service-win32.c',
+    'vss-win32.c'
+  ))
+else
+  qga_ss.add(files(
+    'channel-posix.c',
+    'commands-posix.c',
+    'commands-posix-ssh.c',
+  ))
+  if targetos == 'linux'
+    qga_ss.add(files('commands-linux.c'))
+  elif targetos in bsd_oses
+    qga_ss.add(files('commands-bsd.c'))
+  endif
 endif
-qga_ss.add(when: 'CONFIG_WIN32', if_true: files(
-  'channel-win32.c',
-  'commands-win32.c',
-  'service-win32.c',
-  'vss-win32.c'
-))
 
 qga_ss = qga_ss.apply(config_targetos, strict: false)
 
diff --git a/ui/meson.build b/ui/meson.build
index 8379a78..a370494 100644
--- a/ui/meson.build
+++ b/ui/meson.build
@@ -105,7 +105,9 @@
 endif
 
 if gtk.found()
-  system_ss.add(when: 'CONFIG_WIN32', if_true: files('win32-kbd-hook.c'))
+  if targetos == 'windows'
+    system_ss.add(files('win32-kbd-hook.c'))
+  endif
 
   gtk_ss = ss.source_set()
   gtk_ss.add(gtk, vte, pixman, files('gtk.c'))
@@ -119,7 +121,9 @@
 endif
 
 if sdl.found()
-  system_ss.add(when: 'CONFIG_WIN32', if_true: files('win32-kbd-hook.c'))
+  if targetos == 'windows'
+    system_ss.add(files('win32-kbd-hook.c'))
+  endif
 
   sdl_ss = ss.source_set()
   sdl_ss.add(sdl, sdl_image, pixman, glib, files(
diff --git a/util/meson.build b/util/meson.build
index 98dd7fa..4e970d2 100644
--- a/util/meson.build
+++ b/util/meson.build
@@ -3,28 +3,31 @@
 if not config_host_data.get('CONFIG_ATOMIC64')
   util_ss.add(files('atomic64.c'))
 endif
-util_ss.add(when: 'CONFIG_POSIX', if_true: files('aio-posix.c'))
-util_ss.add(when: 'CONFIG_POSIX', if_true: files('fdmon-poll.c'))
-if config_host_data.get('CONFIG_EPOLL_CREATE1')
-  util_ss.add(files('fdmon-epoll.c'))
+if targetos != 'windows'
+  util_ss.add(files('aio-posix.c'))
+  util_ss.add(files('fdmon-poll.c'))
+  if config_host_data.get('CONFIG_EPOLL_CREATE1')
+    util_ss.add(files('fdmon-epoll.c'))
+  endif
+  util_ss.add(files('compatfd.c'))
+  util_ss.add(files('event_notifier-posix.c'))
+  util_ss.add(files('mmap-alloc.c'))
+  freebsd_dep = []
+  if targetos == 'freebsd'
+    freebsd_dep = util
+  endif
+  util_ss.add(files('oslib-posix.c'), freebsd_dep)
+  util_ss.add(files('qemu-thread-posix.c'))
+  util_ss.add(files('memfd.c'))
+  util_ss.add(files('drm.c'))
+else
+  util_ss.add(files('aio-win32.c'))
+  util_ss.add(files('event_notifier-win32.c'))
+  util_ss.add(files('oslib-win32.c'))
+  util_ss.add(files('qemu-thread-win32.c'))
+  util_ss.add(winmm, pathcch)
 endif
 util_ss.add(when: linux_io_uring, if_true: files('fdmon-io_uring.c'))
-util_ss.add(when: 'CONFIG_POSIX', if_true: files('compatfd.c'))
-util_ss.add(when: 'CONFIG_POSIX', if_true: files('event_notifier-posix.c'))
-util_ss.add(when: 'CONFIG_POSIX', if_true: files('mmap-alloc.c'))
-freebsd_dep = []
-if targetos == 'freebsd'
-  freebsd_dep = util
-endif
-util_ss.add(when: 'CONFIG_POSIX', if_true: [files('oslib-posix.c'), freebsd_dep])
-util_ss.add(when: 'CONFIG_POSIX', if_true: files('qemu-thread-posix.c'))
-util_ss.add(when: 'CONFIG_POSIX', if_true: files('memfd.c'))
-util_ss.add(when: 'CONFIG_WIN32', if_true: files('aio-win32.c'))
-util_ss.add(when: 'CONFIG_WIN32', if_true: files('event_notifier-win32.c'))
-util_ss.add(when: 'CONFIG_WIN32', if_true: files('oslib-win32.c'))
-util_ss.add(when: 'CONFIG_WIN32', if_true: files('qemu-thread-win32.c'))
-util_ss.add(when: 'CONFIG_WIN32', if_true: winmm)
-util_ss.add(when: 'CONFIG_WIN32', if_true: pathcch)
 if glib_has_gslice
   util_ss.add(files('qtree.c'))
 endif
@@ -56,7 +59,6 @@
 util_ss.add(files('stats64.c'))
 util_ss.add(files('systemd.c'))
 util_ss.add(files('transactions.c'))
-util_ss.add(when: 'CONFIG_POSIX', if_true: files('drm.c'))
 util_ss.add(files('guest-random.c'))
 util_ss.add(files('yank.c'))
 util_ss.add(files('int128.c'))