diff --git a/src/bpf_helpers.h b/src/bpf_helpers.h
index f69cc20..60aad05 100644
--- a/src/bpf_helpers.h
+++ b/src/bpf_helpers.h
@@ -2,6 +2,12 @@
 #ifndef __BPF_HELPERS__
 #define __BPF_HELPERS__
 
+/*
+ * Note that bpf programs need to include either
+ * vmlinux.h (auto-generated from BTF) or linux/types.h
+ * in advance since bpf_helper_defs.h uses such types
+ * as __u64.
+ */
 #include "bpf_helper_defs.h"
 
 #define __uint(name, val) int (*name)[val]