diff --git a/meson.build b/meson.build
index 052474895d..376c8b84be 100644
--- a/meson.build
+++ b/meson.build
@@ -54,14 +54,15 @@ endif
 
 #####################################################################
 
+split_usr = get_option('split-usr')
+conf.set10('HAVE_SPLIT_USR', split_usr)
+
 rootprefixdir = get_option('rootprefix')
-conf.set10('HAVE_SPLIT_USR', get_option('split-usr'))
 # Unusual rootprefixdir values are used by some distros
 # (see https://github.com/systemd/systemd/pull/7461).
-if get_option('split-usr')
-        rootprefixdir = rootprefixdir != '' ? rootprefixdir : '/'
-else
-        rootprefixdir = rootprefixdir != '' ? rootprefixdir : '/usr'
+rootprefix_default = get_option('split-usr') ? '/' : '/usr'
+if rootprefixdir == ''
+        rootprefixdir = rootprefix_default
 endif
 
 sysvinit_path = get_option('sysvinit-path')
@@ -2615,3 +2616,10 @@ status += [
         'disabled features: @0@'.format(', '.join(missing)),
         '']
 message('\n         '.join(status))
+
+if rootprefixdir != rootprefix_default
+        message('WARNING:\n' +
+                '        Note that the installation prefix was changed to "@0@".\n'.format(rootprefixdir) +
+                '        systemd used fixed names for unit file directories and other paths, so anything\n' +
+                '        except the default ("@0@") is strongly discouraged.'.format(rootprefix_default))
+endif