diff --git a/file.c b/file.c
index 08cd5f8..45e0a17 100644
--- a/file.c
+++ b/file.c
@@ -1022,6 +1022,11 @@ rb_group_member(GETGROUPS_T gid)
 	return TRUE;
 
 # ifdef HAVE_GETGROUPS
+#  ifdef NGROUPS
+#    if NGROUPS < 32
+#      define NGROUPS 32
+#    endif
+#  endif
 #  ifndef NGROUPS
 #   ifdef NGROUPS_MAX
 #    define NGROUPS NGROUPS_MAX