diff --git a/coregrind/pub_core_mallocfree.h b/coregrind/pub_core_mallocfree.h
index 8281e4d..f63a7e6 100644
--- a/coregrind/pub_core_mallocfree.h
+++ b/coregrind/pub_core_mallocfree.h
@@ -97,9 +97,6 @@
 extern Char* VG_(arena_strdup)  ( ArenaId aid, HChar* cc, 
                                   const Char* s);
 
-// Nb: The ThreadId doesn't matter, it's not used.
-extern SizeT VG_(arena_payload_szB) ( ThreadId tid, ArenaId aid, void* payload );
-
 extern SizeT VG_(arena_malloc_usable_size) ( ArenaId aid, void* payload );
 
 extern void  VG_(mallinfo) ( ThreadId tid, struct vg_mallinfo* mi );