diff --git a/src/core/lib/Base64.mjs b/src/core/lib/Base64.mjs
index dd4ab878..9e721bf6 100755
--- a/src/core/lib/Base64.mjs
+++ b/src/core/lib/Base64.mjs
@@ -81,6 +81,7 @@ export function fromBase64(data, alphabet="A-Za-z0-9+/=", returnType="string", r
         return returnType === "string" ? "" : [];
     }
 
+    alphabet = alphabet || "A-Za-z0-9+/=";
     alphabet = Utils.expandAlphRange(alphabet).join("");
 
     const output = [];
diff --git a/src/core/operations/ShowBase64Offsets.mjs b/src/core/operations/ShowBase64Offsets.mjs
index 62b8b481..d028400d 100644
--- a/src/core/operations/ShowBase64Offsets.mjs
+++ b/src/core/operations/ShowBase64Offsets.mjs
@@ -36,6 +36,11 @@ class ShowBase64Offsets extends Operation {
                 name: "Show variable chars and padding",
                 type: "boolean",
                 value: true
+            },
+            {
+                name: "Input format",
+                type: "option",
+                value: ["Raw", "Base64"]
             }
         ];
     }
@@ -46,7 +51,11 @@ class ShowBase64Offsets extends Operation {
      * @returns {html}
      */
     run(input, args) {
-        const [alphabet, showVariable] = args;
+        const [alphabet, showVariable, format] = args;
+
+        if (format === "Base64") {
+            input = fromBase64(Utils.byteArrayToUtf8(input), null, "byteArray");
+        }
 
         let offset0 = toBase64(input, alphabet),
             offset1 = toBase64([0].concat(input), alphabet),