diff --git a/app/flatpak-builtins-config.c b/app/flatpak-builtins-config.c
index 6fb40952..b491b12f 100644
--- a/app/flatpak-builtins-config.c
+++ b/app/flatpak-builtins-config.c
@@ -51,6 +51,10 @@ looks_like_a_language (const char *s)
   int len = strlen (s);
   int i;
 
+  if (g_str_equal (s, "C") ||
+      g_str_equal (s, "POSIX"))
+    return TRUE;
+
   if (len < 2 || len > 3)
     return FALSE;