diff --git a/meson.build b/meson.build
--- a/meson.build
+++ b/meson.build
@@ -84,7 +84,45 @@
 else
   elogind_dep = dependency('libelogind')
   logind_dep = elogind_dep
-  have_userdb = false
-  greeter_uid_min = 0
-  greeter_uid_max = 0
+
+  # Check that elogind provides the Varlink and JSON headers required by GDM.
+  have_sd_varlink = cc.has_header(
+    'systemd/sd-varlink.h',
+    dependencies: elogind_dep
+  )
+
+  have_sd_json = cc.has_header(
+    'systemd/sd-json.h',
+    dependencies: elogind_dep
+  )
+
+  have_userdb = have_sd_varlink and have_sd_json
+
+  # Check that the required Varlink and JSON API can be linked.
+  if have_userdb
+    have_userdb = cc.links('''
+      #include <systemd/sd-varlink.h>
+      #include <systemd/sd-json.h>
+
+      int main(void) {
+        sd_varlink_server *server = NULL;
+        sd_json_variant *json = NULL;
+
+        sd_varlink_server_new(&server, SD_VARLINK_SERVER_INHERIT_USERDATA);
+        sd_json_buildo(&json, SD_JSON_BUILD_PAIR_BOOLEAN("test", 1));
+
+        sd_varlink_server_unref(server);
+        sd_json_variant_unref(json);
+        return 0;
+      }
+    ''', dependencies: elogind_dep)
+  endif
+
+  if have_userdb
+    greeter_uid_min = 60578
+    greeter_uid_max = 60705
+  else
+    greeter_uid_min = 0
+    greeter_uid_max = 0
+  endif
 endif