diff --git a/meson.build b/meson.build
index 2e76d44aeb..b0d22d5a18 100644
--- a/meson.build
+++ b/meson.build
@@ -405,6 +405,7 @@ possible_common_cc_flags = [
         '-Werror=shift-overflow=2',
         '-Werror=strict-flex-arrays',
         '-Werror=undef',
+        '-Werror=unused-variable',
         '-Wfloat-equal',
         # gperf prevents us from enabling this because it does not emit fallthrough
         # attribute with clang.
@@ -2364,9 +2365,9 @@ subdir('src/login')
 subdir('src/machine')
 subdir('src/machine-id-setup')
 subdir('src/measure')
-subdir('src/mountfsd')
 subdir('src/modules-load')
 subdir('src/mount')
+subdir('src/mountfsd')
 subdir('src/network')
 subdir('src/notify')
 subdir('src/nspawn')
@@ -2400,6 +2401,7 @@ subdir('src/socket-activate')
 subdir('src/socket-proxy')
 subdir('src/ssh-generator')
 subdir('src/stdio-bridge')
+subdir('src/storagetm')
 subdir('src/sulogin-shell')
 subdir('src/sysctl')
 subdir('src/sysext')
@@ -2408,7 +2410,6 @@ subdir('src/systemctl')
 subdir('src/sysupdate')
 subdir('src/sysusers')
 subdir('src/sysv-generator')
-subdir('src/storagetm')
 subdir('src/timedate')
 subdir('src/timesync')
 subdir('src/tmpfiles')