diff --git a/src/Cask/Polyfill.cs b/src/Cask/Polyfill.cs
index afb7c5d..44bff92 100644
--- a/src/Cask/Polyfill.cs
+++ b/src/Cask/Polyfill.cs
@@ -175,6 +175,11 @@ public static string ToBase64String(ReadOnlySpan<byte> bytes)
         {
             return Bcl_Convert.ToBase64String(bytes.ToArray());
         }
+
+        public static byte[] FromBase64String(string base64)
+        {
+            return Bcl_Convert.FromBase64String(base64);
+        }
     }
 
     internal static class RandomNumberGenerator