diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5bec9cf..834ec9a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -34,6 +34,7 @@
   that occurs during an out-of-band code update.
 
 - firmware update: Add encode/decode API for downstream device update command
+- base: Add `PLDM_ERROR_UNEXPECTED_TRANSFER_FLAG_OPERATION` completion code
 
 ### Changed
 
diff --git a/include/libpldm/base.h b/include/libpldm/base.h
index 928c564..e5ba4bb 100644
--- a/include/libpldm/base.h
+++ b/include/libpldm/base.h
@@ -57,7 +57,8 @@
 	PLDM_ERROR_NOT_READY = 0x04,
 	PLDM_ERROR_UNSUPPORTED_PLDM_CMD = 0x05,
 	PLDM_ERROR_INVALID_PLDM_TYPE = 0x20,
-	PLDM_INVALID_TRANSFER_OPERATION_FLAG = 0x21
+	PLDM_INVALID_TRANSFER_OPERATION_FLAG = 0x21,
+	PLDM_ERROR_UNEXPECTED_TRANSFER_FLAG_OPERATION = 0x23,
 };
 
 enum transfer_op_flag {