diff --git a/README.md b/README.md
index 8630092..c63af52 100644
--- a/README.md
+++ b/README.md
@@ -167,7 +167,7 @@ logger.fatal(new Error("I am a pretty Error with a stacktrace."));
 ## All Features
 
 - **Universal:** Works in browsers and Node.js
-- **Tested:** 100% code coverage, CI
+- **Tested:** Great code coverage, CI
 - **Super customizable:** Every aspect can be overwritten
 - **Fully typed:** Written in TypeScript, with native TypeScript support
 - **Default log level:** `silly`, `trace`, `debug`, `info`, `warn`, `error`, `fatal` (different colors)
diff --git a/src/runtime/browser/util.inspect.polyfil.ts b/src/runtime/browser/util.inspect.polyfil.ts
index c85de7b..9f15b1f 100644
--- a/src/runtime/browser/util.inspect.polyfil.ts
+++ b/src/runtime/browser/util.inspect.polyfil.ts
@@ -377,7 +377,8 @@ function reduceToSingleString(output: string[], base: string, braces: string[]):
   return braces[0] + (base === "" ? "" : base + "\n") + "  " + output.join(",\n  ") + " " + braces[1];
 }
 
-function _extend(origin: object, add: object) {
+function _extend(origin: object, add: object): object {
+  const typedOrigin = { ...origin } as { [key: string]: unknown };
   // Don't do anything if add isn't an object
   if (!add || !isObject(add)) return origin;
 
@@ -386,9 +387,9 @@ function _extend(origin: object, add: object) {
   const keys = Object.keys(add);
   let i = keys.length;
   while (i--) {
-    origin[keys[i]] = clonedAdd[keys[i]];
+    typedOrigin[keys[i]] = clonedAdd[keys[i]];
   }
-  return origin;
+  return typedOrigin;
 }
 
 export function formatWithOptions(inspectOptions: InspectOptions, ...args: unknown[]) {