diff --git a/lib/prototypes/README.md b/lib/PROTOTYPES.md
similarity index 84%
rename from lib/prototypes/README.md
rename to lib/PROTOTYPES.md
index c3d92fe..acd4893 100644
--- a/lib/prototypes/README.md
+++ b/lib/PROTOTYPES.md
@@ -1,6 +1,6 @@
 # Prototypes
 
-The functions in this folder are to be use for keeping cached references to the built-in prototypes, so that people can't inadvertently break the library by making mistakes in userland.
+The functions in this module are to be used for keeping cached references to the built-in prototypes, so that people can't inadvertently break the library by making mistakes in userland.
 
 See https://github.com/sinonjs/sinon/pull/1523
 
diff --git a/lib/called-in-order.mjs b/lib/called-in-order.mjs
index febd910..4c756f7 100644
--- a/lib/called-in-order.mjs
+++ b/lib/called-in-order.mjs
@@ -1,5 +1,5 @@
-import array from "./prototypes/array.mjs";
-const every = array.every;
+import prototypes from "./prototypes.mjs";
+const every = prototypes.array.every;
 
 /**
  * @private
diff --git a/lib/index.mjs b/lib/index.mjs
index cc1193d..9c2a0ba 100644
--- a/lib/index.mjs
+++ b/lib/index.mjs
@@ -5,7 +5,7 @@ import * as deprecated from "./deprecated.js";
 import every from "./every.mjs";
 import functionName from "./function-name.mjs";
 import orderByFirstCall from "./order-by-first-call.mjs";
-import prototypes from "./prototypes/index.mjs";
+import prototypes from "./prototypes.mjs";
 import typeOf from "./type-of.mjs";
 import valueToString from "./value-to-string.mjs";
 
diff --git a/lib/order-by-first-call.mjs b/lib/order-by-first-call.mjs
index 502b2cb..4646be2 100644
--- a/lib/order-by-first-call.mjs
+++ b/lib/order-by-first-call.mjs
@@ -1,5 +1,5 @@
-import pkg from "./prototypes/array.mjs";
-const { slice, sort } = pkg;
+import prototypes from "./prototypes.mjs";
+const { slice, sort } = prototypes.array;
 
 /**
  * @private
diff --git a/lib/prototypes.mjs b/lib/prototypes.mjs
new file mode 100644
index 0000000..57ef8e3
--- /dev/null
+++ b/lib/prototypes.mjs
@@ -0,0 +1,10 @@
+import copyPrototypeMethods from "./copy-prototype-methods.mjs";
+
+export default {
+    array: copyPrototypeMethods(Array.prototype),
+    function: copyPrototypeMethods(Function.prototype),
+    map: copyPrototypeMethods(Map.prototype),
+    object: copyPrototypeMethods(Object.prototype),
+    set: copyPrototypeMethods(Set.prototype),
+    string: copyPrototypeMethods(String.prototype),
+}
diff --git a/lib/prototypes/index.test.mjs b/lib/prototypes.test.mjs
similarity index 72%
rename from lib/prototypes/index.test.mjs
rename to lib/prototypes.test.mjs
index e772e81..c6bf285 100644
--- a/lib/prototypes/index.test.mjs
+++ b/lib/prototypes.test.mjs
@@ -1,15 +1,16 @@
 import pkg from "@sinonjs/referee-sinon";
-const { assert } = pkg;
+const { assert, refute } = pkg;
 
-import throwsOnProto from "../throws-on-proto.mjs";
+import copyPrototypeMethods from "./copy-prototype-methods.mjs";
+import throwsOnProto from "./throws-on-proto.mjs";
+import prototypes from "./prototypes.mjs";
 
-import prototypes from "./index.mjs";
-var arrayProto = prototypes.array;
-var functionProto = prototypes.function;
-var mapProto = prototypes.map;
-var objectProto = prototypes.object;
-var setProto = prototypes.set;
-var stringProto = prototypes.string;
+const arrayProto = prototypes.array;
+const functionProto = prototypes.function;
+const mapProto = prototypes.map;
+const objectProto = prototypes.object;
+const setProto = prototypes.set;
+const stringProto = prototypes.string;
 
 describe("prototypes", function () {
     describe(".array", function () {
@@ -36,6 +37,14 @@ describe("prototypes", function () {
         // eslint-disable-next-line mocha/no-setup-in-describe
         verifyProperties(stringProto, String);
     });
+
+    describe("copyPrototypeMethods", function () {
+        it("does not throw for Map", function () {
+            refute.exception(function () {
+                copyPrototypeMethods(Map.prototype);
+            });
+        });
+    });
 });
 
 function verifyProperties(p, origin) {
diff --git a/lib/prototypes/array.mjs b/lib/prototypes/array.mjs
deleted file mode 100644
index ccbe500..0000000
--- a/lib/prototypes/array.mjs
+++ /dev/null
@@ -1,3 +0,0 @@
-import copyPrototype from "../copy-prototype-methods.mjs";
-
-export default copyPrototype(Array.prototype);
diff --git a/lib/prototypes/function.mjs b/lib/prototypes/function.mjs
deleted file mode 100644
index 897a6ff..0000000
--- a/lib/prototypes/function.mjs
+++ /dev/null
@@ -1,3 +0,0 @@
-import copyPrototype from "../copy-prototype-methods.mjs";
-
-export default copyPrototype(Function.prototype);
diff --git a/lib/prototypes/index.mjs b/lib/prototypes/index.mjs
deleted file mode 100644
index e063985..0000000
--- a/lib/prototypes/index.mjs
+++ /dev/null
@@ -1,15 +0,0 @@
-import array from "./array.mjs";
-import func from "./function.mjs";
-import map from "./map.mjs";
-import object from "./object.mjs";
-import set from "./set.mjs";
-import string from "./string.mjs";
-
-export default {
-    array,
-    function: func,
-    map,
-    object,
-    set,
-    string,
-};
diff --git a/lib/prototypes/map.mjs b/lib/prototypes/map.mjs
deleted file mode 100644
index e3d0781..0000000
--- a/lib/prototypes/map.mjs
+++ /dev/null
@@ -1,3 +0,0 @@
-import copyPrototype from "../copy-prototype-methods.mjs";
-
-export default copyPrototype(Map.prototype);
diff --git a/lib/prototypes/object.mjs b/lib/prototypes/object.mjs
deleted file mode 100644
index 5dc4d7b..0000000
--- a/lib/prototypes/object.mjs
+++ /dev/null
@@ -1,3 +0,0 @@
-import copyPrototype from "../copy-prototype-methods.mjs";
-
-export default copyPrototype(Object.prototype);
diff --git a/lib/prototypes/set.mjs b/lib/prototypes/set.mjs
deleted file mode 100644
index ec6f658..0000000
--- a/lib/prototypes/set.mjs
+++ /dev/null
@@ -1,3 +0,0 @@
-import copyPrototype from "../copy-prototype-methods.mjs";
-
-export default copyPrototype(Set.prototype);
diff --git a/lib/prototypes/string.mjs b/lib/prototypes/string.mjs
deleted file mode 100644
index 8598723..0000000
--- a/lib/prototypes/string.mjs
+++ /dev/null
@@ -1,3 +0,0 @@
-import copyPrototype from "../copy-prototype-methods.mjs";
-
-export default copyPrototype(String.prototype);