diff --git a/doc/api/util.md b/doc/api/util.md
index 88e2f34b7c8b26..f4e689a2130bd5 100644
--- a/doc/api/util.md
+++ b/doc/api/util.md
@@ -398,6 +398,10 @@ stream.write('With ES6');
 <!-- YAML
 added: v0.3.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/30768
+    description: User defined prototype properties are inspected in case
+                 `showHidden` is `true`.
   - version: v13.0.0
     pr-url: https://github.com/nodejs/node/pull/27685
     description: Circular references now include a marker to the reference.
@@ -461,7 +465,8 @@ changes:
 * `options` {Object}
   * `showHidden` {boolean} If `true`, `object`'s non-enumerable symbols and
     properties are included in the formatted result. [`WeakMap`][] and
-    [`WeakSet`][] entries are also included. **Default:** `false`.
+    [`WeakSet`][] entries are also included as well as user defined prototype
+    properties (excluding method properties). **Default:** `false`.
   * `depth` {number} Specifies the number of times to recurse while formatting
     `object`. This is useful for inspecting large objects. To recurse up to
     the maximum call stack size pass `Infinity` or `null`.
diff --git a/lib/internal/util/inspect.js b/lib/internal/util/inspect.js
index 8e2c0a71613f44..1dc09a8aa06020 100644
--- a/lib/internal/util/inspect.js
+++ b/lib/internal/util/inspect.js
@@ -448,7 +448,7 @@ function getEmptyFormatArray() {
   return [];
 }
 
-function getConstructorName(obj, ctx, recurseTimes) {
+function getConstructorName(obj, ctx, recurseTimes, protoProps) {
   let firstProto;
   const tmp = obj;
   while (obj) {
@@ -456,6 +456,12 @@ function getConstructorName(obj, ctx, recurseTimes) {
     if (descriptor !== undefined &&
         typeof descriptor.value === 'function' &&
         descriptor.value.name !== '') {
+      if (protoProps !== undefined &&
+          !builtInObjects.has(descriptor.value.name)) {
+        const isProto = firstProto !== undefined;
+        addPrototypeProperties(
+          ctx, tmp, obj, recurseTimes, isProto, protoProps);
+      }
       return descriptor.value.name;
     }
 
@@ -475,7 +481,8 @@ function getConstructorName(obj, ctx, recurseTimes) {
     return `${res} <Complex prototype>`;
   }
 
-  const protoConstr = getConstructorName(firstProto, ctx, recurseTimes + 1);
+  const protoConstr = getConstructorName(
+    firstProto, ctx, recurseTimes + 1, protoProps);
 
   if (protoConstr === null) {
     return `${res} <${inspect(firstProto, {
@@ -488,6 +495,68 @@ function getConstructorName(obj, ctx, recurseTimes) {
   return `${res} <${protoConstr}>`;
 }
 
+// This function has the side effect of adding prototype properties to the
+// `output` argument (which is an array). This is intended to highlight user
+// defined prototype properties.
+function addPrototypeProperties(ctx, main, obj, recurseTimes, isProto, output) {
+  let depth = 0;
+  let keys;
+  let keySet;
+  do {
+    if (!isProto) {
+      obj = ObjectGetPrototypeOf(obj);
+      // Stop as soon as a null prototype is encountered.
+      if (obj === null) {
+        return;
+      }
+      // Stop as soon as a built-in object type is detected.
+      const descriptor = ObjectGetOwnPropertyDescriptor(obj, 'constructor');
+      if (descriptor !== undefined &&
+          typeof descriptor.value === 'function' &&
+          builtInObjects.has(descriptor.value.name)) {
+        return;
+      }
+    } else {
+      isProto = false;
+    }
+
+    if (depth === 0) {
+      keySet = new Set();
+    } else {
+      keys.forEach((key) => keySet.add(key));
+    }
+    // Get all own property names and symbols.
+    keys = ObjectGetOwnPropertyNames(obj);
+    const symbols = ObjectGetOwnPropertySymbols(obj);
+    if (symbols.length !== 0) {
+      keys.push(...symbols);
+    }
+    for (const key of keys) {
+      // Ignore the `constructor` property and keys that exist on layers above.
+      if (key === 'constructor' ||
+          ObjectPrototypeHasOwnProperty(main, key) ||
+          (depth !== 0 && keySet.has(key))) {
+        continue;
+      }
+      const desc = ObjectGetOwnPropertyDescriptor(obj, key);
+      if (typeof desc.value === 'function') {
+        continue;
+      }
+      const value = formatProperty(
+        ctx, obj, recurseTimes, key, kObjectType, desc);
+      if (ctx.colors) {
+        // Faint!
+        output.push(`\u001b[2m${value}\u001b[22m`);
+      } else {
+        output.push(value);
+      }
+    }
+  // Limit the inspection to up to three prototype layers. Using `recurseTimes`
+  // is not a good choice here, because it's as if the properties are declared
+  // on the current object from the users perspective.
+  } while (++depth !== 3);
+}
+
 function getPrefix(constructor, tag, fallback) {
   if (constructor === null) {
     if (tag !== '') {
@@ -691,8 +760,17 @@ function formatValue(ctx, value, recurseTimes, typedArray) {
 
 function formatRaw(ctx, value, recurseTimes, typedArray) {
   let keys;
+  let protoProps;
+  if (ctx.showHidden && (recurseTimes <= ctx.depth || ctx.depth === null)) {
+    protoProps = [];
+  }
+
+  const constructor = getConstructorName(value, ctx, recurseTimes, protoProps);
+  // Reset the variable to check for this later on.
+  if (protoProps !== undefined && protoProps.length === 0) {
+    protoProps = undefined;
+  }
 
-  const constructor = getConstructorName(value, ctx, recurseTimes);
   let tag = value[SymbolToStringTag];
   // Only list the tag in case it's non-enumerable / not an own property.
   // Otherwise we'd print this twice.
@@ -722,21 +800,21 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
       // Only set the constructor for non ordinary ("Array [...]") arrays.
       const prefix = getPrefix(constructor, tag, 'Array');
       braces = [`${prefix === 'Array ' ? '' : prefix}[`, ']'];
-      if (value.length === 0 && keys.length === 0)
+      if (value.length === 0 && keys.length === 0 && protoProps === undefined)
         return `${braces[0]}]`;
       extrasType = kArrayExtrasType;
       formatter = formatArray;
     } else if (isSet(value)) {
       keys = getKeys(value, ctx.showHidden);
       const prefix = getPrefix(constructor, tag, 'Set');
-      if (value.size === 0 && keys.length === 0)
+      if (value.size === 0 && keys.length === 0 && protoProps === undefined)
         return `${prefix}{}`;
       braces = [`${prefix}{`, '}'];
       formatter = formatSet;
     } else if (isMap(value)) {
       keys = getKeys(value, ctx.showHidden);
       const prefix = getPrefix(constructor, tag, 'Map');
-      if (value.size === 0 && keys.length === 0)
+      if (value.size === 0 && keys.length === 0 && protoProps === undefined)
         return `${prefix}{}`;
       braces = [`${prefix}{`, '}'];
       formatter = formatMap;
@@ -771,12 +849,12 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
       } else if (tag !== '') {
         braces[0] = `${getPrefix(constructor, tag, 'Object')}{`;
       }
-      if (keys.length === 0) {
+      if (keys.length === 0 && protoProps === undefined) {
         return `${braces[0]}}`;
       }
     } else if (typeof value === 'function') {
       base = getFunctionBase(value, constructor, tag);
-      if (keys.length === 0)
+      if (keys.length === 0 && protoProps === undefined)
         return ctx.stylize(base, 'special');
     } else if (isRegExp(value)) {
       // Make RegExps say that they are RegExps
@@ -786,8 +864,10 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
       const prefix = getPrefix(constructor, tag, 'RegExp');
       if (prefix !== 'RegExp ')
         base = `${prefix}${base}`;
-      if (keys.length === 0 || (recurseTimes > ctx.depth && ctx.depth !== null))
+      if ((keys.length === 0 && protoProps === undefined) ||
+          (recurseTimes > ctx.depth && ctx.depth !== null)) {
         return ctx.stylize(base, 'regexp');
+      }
     } else if (isDate(value)) {
       // Make dates with properties first say the date
       base = NumberIsNaN(DatePrototypeGetTime(value)) ?
@@ -796,12 +876,12 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
       const prefix = getPrefix(constructor, tag, 'Date');
       if (prefix !== 'Date ')
         base = `${prefix}${base}`;
-      if (keys.length === 0) {
+      if (keys.length === 0 && protoProps === undefined) {
         return ctx.stylize(base, 'date');
       }
     } else if (isError(value)) {
       base = formatError(value, constructor, tag, ctx);
-      if (keys.length === 0)
+      if (keys.length === 0 && protoProps === undefined)
         return base;
     } else if (isAnyArrayBuffer(value)) {
       // Fast path for ArrayBuffer and SharedArrayBuffer.
@@ -812,7 +892,7 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
       const prefix = getPrefix(constructor, tag, arrayType);
       if (typedArray === undefined) {
         formatter = formatArrayBuffer;
-      } else if (keys.length === 0) {
+      } else if (keys.length === 0 && protoProps === undefined) {
         return prefix +
               `{ byteLength: ${formatNumber(ctx.stylize, value.byteLength)} }`;
       }
@@ -836,7 +916,7 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
       formatter = formatNamespaceObject;
     } else if (isBoxedPrimitive(value)) {
       base = getBoxedBase(value, ctx, keys, constructor, tag);
-      if (keys.length === 0) {
+      if (keys.length === 0 && protoProps === undefined) {
         return base;
       }
     } else {
@@ -856,7 +936,7 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
         formatter = formatIterator;
       // Handle other regular objects again.
       } else {
-        if (keys.length === 0) {
+        if (keys.length === 0 && protoProps === undefined) {
           if (isExternal(value))
             return ctx.stylize('[External]', 'special');
           return `${getCtxStyle(value, constructor, tag)}{}`;
@@ -884,6 +964,9 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
       output.push(
         formatProperty(ctx, value, recurseTimes, keys[i], extrasType));
     }
+    if (protoProps !== undefined) {
+      output.push(...protoProps);
+    }
   } catch (err) {
     const constructorName = getCtxStyle(value, constructor, tag).slice(0, -1);
     return handleMaxCallStackSize(ctx, err, constructorName, indentationLvl);
@@ -1350,6 +1433,7 @@ function formatTypedArray(ctx, value, recurseTimes) {
   }
   if (ctx.showHidden) {
     // .buffer goes last, it's not a primitive like the others.
+    // All besides `BYTES_PER_ELEMENT` are actually getters.
     ctx.indentationLvl += 2;
     for (const key of [
       'BYTES_PER_ELEMENT',
@@ -1498,10 +1582,10 @@ function formatPromise(ctx, value, recurseTimes) {
   return output;
 }
 
-function formatProperty(ctx, value, recurseTimes, key, type) {
+function formatProperty(ctx, value, recurseTimes, key, type, desc) {
   let name, str;
   let extra = ' ';
-  const desc = ObjectGetOwnPropertyDescriptor(value, key) ||
+  desc = desc || ObjectGetOwnPropertyDescriptor(value, key) ||
     { value: value[key], enumerable: true };
   if (desc.value !== undefined) {
     const diff = (type !== kObjectType || ctx.compact !== true) ? 2 : 3;
diff --git a/test/parallel/test-util-inspect.js b/test/parallel/test-util-inspect.js
index 4355e615c4fb0b..098aee4adc9bb6 100644
--- a/test/parallel/test-util-inspect.js
+++ b/test/parallel/test-util-inspect.js
@@ -391,8 +391,24 @@ assert.strictEqual(
 {
   class CustomArray extends Array {}
   CustomArray.prototype[5] = 'foo';
+  CustomArray.prototype[49] = 'bar';
+  CustomArray.prototype.foo = true;
   const arr = new CustomArray(50);
-  assert.strictEqual(util.inspect(arr), 'CustomArray [ <50 empty items> ]');
+  arr[49] = 'I win';
+  assert.strictEqual(
+    util.inspect(arr),
+    "CustomArray [ <49 empty items>, 'I win' ]"
+  );
+  assert.strictEqual(
+    util.inspect(arr, { showHidden: true }),
+    'CustomArray [\n' +
+    '  <49 empty items>,\n' +
+    "  'I win',\n" +
+    '  [length]: 50,\n' +
+    "  '5': 'foo',\n" +
+    '  foo: true\n' +
+    ']'
+  );
 }
 
 // Array with extra properties.
@@ -2588,3 +2604,65 @@ assert.strictEqual(
       throw err;
   }
 }
+
+// Inspect prototype properties.
+{
+  class Foo extends Map {
+    prop = false;
+    prop2 = true;
+    get abc() {
+      return true;
+    }
+    get def() {
+      return false;
+    }
+    set def(v) {}
+    get xyz() {
+      return 'Should be ignored';
+    }
+    func(a) {}
+    [util.inspect.custom]() {
+      return this;
+    }
+  }
+
+  class Bar extends Foo {
+    abc = true;
+    prop = true;
+    get xyz() {
+      return 'YES!';
+    }
+    [util.inspect.custom]() {
+      return this;
+    }
+  }
+
+  const bar = new Bar();
+
+  assert.strictEqual(
+    inspect(bar),
+    'Bar [Map] { prop: true, prop2: true, abc: true }'
+  );
+  assert.strictEqual(
+    inspect(bar, { showHidden: true, getters: true, colors: false }),
+    'Bar [Map] {\n' +
+    '  [size]: 0,\n' +
+    '  prop: true,\n' +
+    '  prop2: true,\n' +
+    '  abc: true,\n' +
+    "  [xyz]: [Getter: 'YES!'],\n" +
+    '  [def]: [Getter/Setter: false]\n' +
+    '}'
+  );
+  assert.strictEqual(
+    inspect(bar, { showHidden: true, getters: false, colors: true }),
+    'Bar [Map] {\n' +
+    '  [size]: \x1B[33m0\x1B[39m,\n' +
+    '  prop: \x1B[33mtrue\x1B[39m,\n' +
+    '  prop2: \x1B[33mtrue\x1B[39m,\n' +
+    '  abc: \x1B[33mtrue\x1B[39m,\n' +
+    '  \x1B[2m[xyz]: \x1B[36m[Getter]\x1B[39m\x1B[22m,\n' +
+    '  \x1B[2m[def]: \x1B[36m[Getter/Setter]\x1B[39m\x1B[22m\n' +
+    '}'
+  );
+}
diff --git a/test/parallel/test-whatwg-encoding-custom-textdecoder.js b/test/parallel/test-whatwg-encoding-custom-textdecoder.js
index e3779a945de4a9..c475d94dc7acd1 100644
--- a/test/parallel/test-whatwg-encoding-custom-textdecoder.js
+++ b/test/parallel/test-whatwg-encoding-custom-textdecoder.js
@@ -113,10 +113,19 @@ if (common.hasIntl) {
   } else {
     assert.strictEqual(
       util.inspect(dec, { showHidden: true }),
-      "TextDecoder {\n  encoding: 'utf-8',\n  fatal: false,\n  " +
-      'ignoreBOM: true,\n  [Symbol(flags)]: 4,\n  [Symbol(handle)]: ' +
-      "StringDecoder {\n    encoding: 'utf8',\n    " +
-      '[Symbol(kNativeDecoder)]: <Buffer 00 00 00 00 00 00 01>\n  }\n}'
+      'TextDecoder {\n' +
+      "  encoding: 'utf-8',\n" +
+      '  fatal: false,\n' +
+      '  ignoreBOM: true,\n' +
+      '  [Symbol(flags)]: 4,\n' +
+      '  [Symbol(handle)]: StringDecoder {\n' +
+      "    encoding: 'utf8',\n" +
+      '    [Symbol(kNativeDecoder)]: <Buffer 00 00 00 00 00 00 01>,\n' +
+      '    lastChar: [Getter],\n' +
+      '    lastNeed: [Getter],\n' +
+      '    lastTotal: [Getter]\n' +
+      '  }\n' +
+      '}'
     );
   }
 }