diff --git a/libc/include/sys/vfs.h b/libc/include/sys/vfs.h
index 3579799..1a640ba 100644
--- a/libc/include/sys/vfs.h
+++ b/libc/include/sys/vfs.h
@@ -40,6 +40,8 @@
 typedef __fsid_t fsid_t;
 
 #if defined(__LP64__)
+/* We can't just use the kernel struct statfs directly here because
+ * it's reused for both struct statfs *and* struct statfs64. */
 #define __STATFS64_BODY \
   uint64_t f_type; \
   uint64_t f_bsize; \