diff --git a/contracts/utils/Base64.sol b/contracts/utils/Base64.sol
index f5e0b1722..b6df0460f 100644
--- a/contracts/utils/Base64.sol
+++ b/contracts/utils/Base64.sol
@@ -4,6 +4,8 @@ pragma solidity ^0.8.0;
 
 /**
  * @dev Provides a set of functions to operate with Base64 strings.
+ *
+ * _Available since v4.5._
  */
 library Base64 {
     /**