diff --git a/tests/lib/libc/db/t_db.sh b/tests/lib/libc/db/t_db.sh
index a16843a0d..f9d9780fd 100644
--- a/tests/lib/libc/db/t_db.sh
+++ b/tests/lib/libc/db/t_db.sh
@@ -866,7 +866,8 @@ bsize_ffactor_body()
 	h_bsize_ffactor 8192 683
 }
 
-# FIXME: what does it test?
+# Verify hash database behavior when inserting 4-character keys and values
+# into a 65536-bucket hash.
 atf_test_case four_char_hash
 four_char_hash_head()
 {