diff --git a/dbus/dbus-sysdeps-unix.c b/dbus/dbus-sysdeps-unix.c
index 2ce425d0..099637cb 100644
--- a/dbus/dbus-sysdeps-unix.c
+++ b/dbus/dbus-sysdeps-unix.c
@@ -1932,6 +1932,8 @@ add_groups_to_credentials (int              client_fd,
 {
 #if defined(__linux__) && defined(SO_PEERGROUPS)
   _DBUS_STATIC_ASSERT (sizeof (gid_t) <= sizeof (dbus_gid_t));
+  /* This function assumes socklen_t is unsigned, which is true on Linux */
+  _DBUS_STATIC_ASSERT (((socklen_t) -1) > 0);
   gid_t *buf = NULL;
   socklen_t len = 1024;
   dbus_bool_t oom = FALSE;