diff --git a/samples/damon/mtier.c b/samples/damon/mtier.c
index d1123ebbfab9..bea45c87cc9b 100644
--- a/samples/damon/mtier.c
+++ b/samples/damon/mtier.c
@@ -52,6 +52,11 @@ module_param(detect_node_addresses, bool, 0600);
 
 static struct damon_ctx *ctxs[2];
 
+/*
+ * Use phys_addr_t instead of damon_addr_range (unsigned long) for physical
+ * addresses.  On 32-bit systems with more than 4GB memory, phys_addr_t will
+ * be 64-bit while unsigned long is 32-bit.
+ */
 struct region_range {
 	phys_addr_t start;
 	phys_addr_t end;