diff --git a/lib/sinon/util/core/format.js b/lib/sinon/util/core/format.js
deleted file mode 100644
index 033c145d7..000000000
--- a/lib/sinon/util/core/format.js
+++ /dev/null
@@ -1,22 +0,0 @@
-"use strict";
-
-var inspect = require("util").inspect;
-var customFormatter;
-
-function format() {
-    if (customFormatter) {
-        return customFormatter.apply(null, arguments);
-    }
-
-    return inspect.apply(inspect, arguments);
-}
-
-format.setFormatter = function (aCustomFormatter) {
-    if (typeof aCustomFormatter !== "function") {
-        throw new Error("format.setFormatter must be called with a function");
-    }
-
-    customFormatter = aCustomFormatter;
-};
-
-module.exports = format;
diff --git a/test/util/core/format-test.js b/test/util/core/format-test.js
deleted file mode 100644
index 6eaed189c..000000000
--- a/test/util/core/format-test.js
+++ /dev/null
@@ -1,33 +0,0 @@
-"use strict";
-
-var referee = require("@sinonjs/referee");
-var sinon = require("../../../lib/sinon");
-var format = require("../../../lib/sinon/util/core/format");
-var assert = referee.assert;
-
-describe("util/core/format", function () {
-    describe("format.setFormatter", function () {
-        it("sets custom formatter", function () {
-            format.setFormatter(function () {
-                return "formatted";
-            });
-            assert.equals(format("Hey"), "formatted");
-        });
-
-        it("throws if custom formatter is not a function", function () {
-            assert.exception(
-                function () {
-                    format.setFormatter("foo");
-                },
-                {
-                    message:
-                        "format.setFormatter must be called with a function",
-                }
-            );
-        });
-
-        it("exposes method on sinon", function () {
-            assert.equals(sinon.setFormatter, format.setFormatter);
-        });
-    });
-});