diff --git a/api/api_full.go b/api/api_full.go
index 63a7e81f7..41efa8077 100644
--- a/api/api_full.go
+++ b/api/api_full.go
@@ -67,6 +67,17 @@ type FullNode interface {
 	ChainGetTipSet(context.Context, types.TipSetKey) (*types.TipSet, error)
 
 	// ChainGetBlockMessages returns messages stored in the specified block.
+	//
+	// Note: If there are multiple blocks in a tipset, it's likely that some
+	// messages will be duplicated. It's also possible for blocks in a tipset to have
+	// different messages from the same sender at the same nonce. When that happens,
+	// only the first message (in a block with lowest ticket) will be considered
+	// for execution
+	//
+	// NOTE: THIS METHOD SHOULD ONLY BE USED FOR GETTING MESSAGES IN A SPECIFIC BLOCK
+	//
+	// DO NOT USE THIS METHOD TO GET MESSAGES INCLUDED IN A TIPSET
+	// Use ChainGetParentMessages, which will perform correct message deduplication
 	ChainGetBlockMessages(ctx context.Context, blockCid cid.Cid) (*BlockMessages, error)
 
 	// ChainGetParentReceipts returns receipts for messages in parent tipset of
diff --git a/documentation/en/api-methods.md b/documentation/en/api-methods.md
index 458210bf8..d0e1bc22e 100644
--- a/documentation/en/api-methods.md
+++ b/documentation/en/api-methods.md
@@ -425,6 +425,17 @@ Response:
 ### ChainGetBlockMessages
 ChainGetBlockMessages returns messages stored in the specified block.
 
+Note: If there are multiple blocks in a tipset, it's likely that some
+messages will be duplicated. It's also possible for blocks in a tipset to have
+different messages from the same sender at the same nonce. When that happens,
+only the first message (in a block with lowest ticket) will be considered
+for execution
+
+NOTE: THIS METHOD SHOULD ONLY BE USED FOR GETTING MESSAGES IN A SPECIFIC BLOCK
+
+DO NOT USE THIS METHOD TO GET MESSAGES INCLUDED IN A TIPSET
+Use ChainGetParentMessages, which will perform correct message deduplication
+
 
 Perms: read