diff --git a/src/core/operations/Jsonata.mjs b/src/core/operations/Jsonata.mjs
index 82cc4d3976..04259343ae 100644
--- a/src/core/operations/Jsonata.mjs
+++ b/src/core/operations/Jsonata.mjs
@@ -51,6 +51,18 @@ class JsonataQuery extends Operation {
 
         try {
             const expression = jsonata(query);
+            // Override built-in base64 functions which fail in Web Worker
+            // context where `window` is undefined. The jsonata library falls
+            // back to `global.Buffer` which also does not exist in workers.
+            // `atob`/`btoa` are available in both browser and worker scopes.
+            expression.registerFunction("base64decode", (str) => {
+                if (typeof str === "undefined") return undefined;
+                return atob(str);
+            }, "<s-:s>");
+            expression.registerFunction("base64encode", (str) => {
+                if (typeof str === "undefined") return undefined;
+                return btoa(str);
+            }, "<s-:s>");
             result = await expression.evaluate(jsonObj);
         } catch (err) {
             throw new OperationError(
diff --git a/tests/browser/02_ops.js b/tests/browser/02_ops.js
index 5ab55451bd..0baded8229 100644
--- a/tests/browser/02_ops.js
+++ b/tests/browser/02_ops.js
@@ -218,6 +218,7 @@ module.exports = {
         testOpHtml(browser, "JSON Beautify", "{a:1}", ".json-dict .json-literal", "1");
         // testOp(browser, "JSON Minify", "test input", "test_output");
     // testOp(browser, "JSON to CSV", "test input", "test_output");
+        testOp(browser, "Jsonata Query", "{}", '"Hello World!"', ['$base64decode("SGVsbG8gV29ybGQh")']);
     // testOp(browser, "JWT Decode", "test input", "test_output");
     // testOp(browser, "JWT Sign", "test input", "test_output");
     // testOp(browser, "JWT Verify", "test input", "test_output");
diff --git a/tests/operations/tests/Jsonata.mjs b/tests/operations/tests/Jsonata.mjs
index fb46a961f2..54ecf34c92 100644
--- a/tests/operations/tests/Jsonata.mjs
+++ b/tests/operations/tests/Jsonata.mjs
@@ -548,4 +548,27 @@ TestRegister.addTests([
             },
         ],
     },
+    // Base64 functions (issue #2063)
+    {
+        name: "Jsonata: $base64decode",
+        input: "{}",
+        expectedOutput: '"Hello World!"',
+        recipeConfig: [
+            {
+                op: "Jsonata Query",
+                args: ['$base64decode("SGVsbG8gV29ybGQh")'],
+            },
+        ],
+    },
+    {
+        name: "Jsonata: $base64encode",
+        input: "{}",
+        expectedOutput: '"SGVsbG8gV29ybGQh"',
+        recipeConfig: [
+            {
+                op: "Jsonata Query",
+                args: ['$base64encode("Hello World!")'],
+            },
+        ],
+    },
 ]);