diff --git a/docs/src/developing/runtime-facilities/sysvars.md b/docs/src/developing/runtime-facilities/sysvars.md
index a72929a68..3b5ed443a 100644
--- a/docs/src/developing/runtime-facilities/sysvars.md
+++ b/docs/src/developing/runtime-facilities/sysvars.md
@@ -97,7 +97,9 @@ other instructions in the same transaction. Read more information on
 ## RecentBlockhashes
 
 The RecentBlockhashes sysvar contains the active recent blockhashes as well as
-their associated fee calculators. It is updated every slot.
+their associated fee calculators. It is updated every slot. Entries are ordered
+by descending block height, so the first entry holds the most recent block hash,
+and the last entry holds an old block hash.
 
 - Address: `SysvarRecentB1ockHashes11111111111111111111`
 - Layout:
diff --git a/sdk/program/src/sysvar/recent_blockhashes.rs b/sdk/program/src/sysvar/recent_blockhashes.rs
index 93fee5e4d..00f822c74 100644
--- a/sdk/program/src/sysvar/recent_blockhashes.rs
+++ b/sdk/program/src/sysvar/recent_blockhashes.rs
@@ -53,6 +53,10 @@ impl<'a> PartialOrd for IterItem<'a> {
     }
 }
 
+/// Contains recent block hashes and fee calculators.
+///
+/// The entries are ordered by descending block height, so the first entry holds
+/// the most recent block hash, and the last entry holds an old block hash.
 #[repr(C)]
 #[derive(Serialize, Deserialize, Clone, Debug, PartialEq)]
 pub struct RecentBlockhashes(Vec<Entry>);