diff --git a/src/dat/nbt.c b/src/dat/nbt.c
index 746742a..8f6ffb2 100644
--- a/src/dat/nbt.c
+++ b/src/dat/nbt.c
@@ -9,6 +9,7 @@
 #include "../util/compat/endian.h"
 #include "../util/intdef.h"
 
+// WARN: does not have public-facing definition
 int nbt_primsize(u8 tag) {
 	switch (tag) {
 	case NBT_I8:  return 1;