https://bugs.gentoo.org/979428
--- a/plugins/perl/meson.build
+++ b/plugins/perl/meson.build
@@ -83,6 +83,7 @@ perl_dep = declare_dependency(
 
 shared_module('perl',
   sources: ['perl.c', hexchat_perl_module, irc_perl_module],
+  c_args: ['-std=gnu99'],
   dependencies: [libgio_dep, hexchat_plugin_dep, perl_dep],
   install: true,
   install_dir: plugindir,