diff --git a/lib/buffer.js b/lib/buffer.js
index d9c64f27cf3e..dcb6f4361ce6 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -1131,6 +1131,13 @@ function bidirectionalIndexOf(buffer, val, byteOffset, end, encoding, dir) {
   }
   dir = !!dir;  // Cast to bool.
 
+  if (typeof end !== 'number') {
+    end = +end;
+    if (NumberIsNaN(end)) {
+      end = buffer.length || buffer.byteLength;
+    }
+  }
+
   if (typeof val === 'number')
     return indexOfNumber(buffer, val >>> 0, byteOffset, dir, end);
 
@@ -1158,7 +1165,7 @@ function bidirectionalIndexOf(buffer, val, byteOffset, end, encoding, dir) {
 }
 
 Buffer.prototype.indexOf = function indexOf(val, offset, end, encoding) {
-  if (typeof end === 'string') {
+  if (encoding === undefined && typeof end !== 'number') {
     encoding = end;
     end = this.length;
   } else if (end === undefined) {
@@ -1168,7 +1175,7 @@ Buffer.prototype.indexOf = function indexOf(val, offset, end, encoding) {
 };
 
 Buffer.prototype.lastIndexOf = function lastIndexOf(val, offset, end, encoding) {
-  if (typeof end === 'string') {
+  if (encoding === undefined && typeof end !== 'number') {
     encoding = end;
     end = this.length;
   } else if (end === undefined) {
@@ -1178,7 +1185,7 @@ Buffer.prototype.lastIndexOf = function lastIndexOf(val, offset, end, encoding)
 };
 
 Buffer.prototype.includes = function includes(val, offset, end, encoding) {
-  if (typeof end === 'string') {
+  if (encoding === undefined && typeof end !== 'number') {
     encoding = end;
     end = this.length;
   } else if (end === undefined) {
diff --git a/test/parallel/test-buffer-indexof-null-encoding.js b/test/parallel/test-buffer-indexof-null-encoding.js
new file mode 100644
index 000000000000..206ec2617a59
--- /dev/null
+++ b/test/parallel/test-buffer-indexof-null-encoding.js
@@ -0,0 +1,86 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+
+const b = Buffer.from('abcdef');
+
+// 3-argument calls: buf.indexOf(val, offset, encoding) where encoding is null
+assert.strictEqual(b.indexOf(0x62, 0, null), 1);
+assert.strictEqual(b.indexOf(Buffer.from('b'), 0, null), 1);
+assert.strictEqual(b.indexOf(new Uint8Array([0x62]), 0, null), 1);
+assert.throws(() => b.indexOf('b', 0, null), {
+  code: 'ERR_UNKNOWN_ENCODING',
+});
+
+// Non-string object encoding in 3-argument calls
+assert.strictEqual(b.indexOf(0x62, 0, {}), 1);
+assert.strictEqual(b.indexOf(Buffer.from('b'), 0, {}), 1);
+assert.throws(() => b.indexOf('b', 0, {}), {
+  code: 'ERR_UNKNOWN_ENCODING',
+});
+
+// 3-argument calls with false encoding
+assert.strictEqual(b.indexOf(0x62, 0, false), 1);
+assert.strictEqual(b.indexOf(Buffer.from('b'), 0, false), 1);
+assert.throws(() => b.indexOf('b', 0, false), {
+  code: 'ERR_UNKNOWN_ENCODING',
+});
+
+// lastIndexOf with null and non-string encoding
+assert.strictEqual(b.lastIndexOf(0x62, 5, null), 1);
+assert.strictEqual(b.lastIndexOf(Buffer.from('b'), 5, null), 1);
+assert.strictEqual(b.lastIndexOf(new Uint8Array([0x62]), 5, null), 1);
+assert.throws(() => b.lastIndexOf('b', 5, null), {
+  code: 'ERR_UNKNOWN_ENCODING',
+});
+assert.strictEqual(b.lastIndexOf(0x62, 5, {}), 1);
+assert.strictEqual(b.lastIndexOf(Buffer.from('b'), 5, {}), 1);
+assert.throws(() => b.lastIndexOf('b', 5, {}), {
+  code: 'ERR_UNKNOWN_ENCODING',
+});
+
+// includes with null and non-string encoding
+assert.strictEqual(b.includes(0x62, 0, null), true);
+assert.strictEqual(b.includes(Buffer.from('b'), 0, null), true);
+assert.strictEqual(b.includes(new Uint8Array([0x62]), 0, null), true);
+assert.throws(() => b.includes('b', 0, null), {
+  code: 'ERR_UNKNOWN_ENCODING',
+});
+assert.strictEqual(b.includes(0x62, 0, {}), true);
+assert.strictEqual(b.includes(Buffer.from('b'), 0, {}), true);
+assert.throws(() => b.includes('b', 0, {}), {
+  code: 'ERR_UNKNOWN_ENCODING',
+});
+
+// 2-argument calls where byteOffset is null
+assert.strictEqual(b.indexOf('b', null), 1);
+assert.strictEqual(b.indexOf(0x62, null), 1);
+assert.strictEqual(b.indexOf(Buffer.from('b'), null), 1);
+assert.strictEqual(b.lastIndexOf('b', null), -1);
+assert.strictEqual(b.lastIndexOf(0x62, null), -1);
+assert.strictEqual(b.lastIndexOf(Buffer.from('b'), null), -1);
+assert.strictEqual(b.includes('b', null), true);
+assert.strictEqual(b.includes(0x62, null), true);
+assert.strictEqual(b.includes(Buffer.from('b'), null), true);
+
+// 3-argument calls where byteOffset is null and encoding is null
+assert.strictEqual(b.indexOf(0x62, null, null), 1);
+assert.strictEqual(b.indexOf(Buffer.from('b'), null, null), 1);
+assert.throws(() => b.indexOf('b', null, null), {
+  code: 'ERR_UNKNOWN_ENCODING',
+});
+assert.strictEqual(b.includes(0x62, null, null), true);
+assert.strictEqual(b.includes(Buffer.from('b'), null, null), true);
+assert.throws(() => b.includes('b', null, null), {
+  code: 'ERR_UNKNOWN_ENCODING',
+});
+
+// 3-argument calls with numeric end bounds still work as expected
+assert.strictEqual(b.indexOf('b', 0, 1), -1);
+assert.strictEqual(b.indexOf('b', 0, 2), 1);
+assert.strictEqual(b.indexOf(0x62, 0, 1), -1);
+assert.strictEqual(b.indexOf(0x62, 0, 2), 1);
+assert.strictEqual(b.indexOf(Buffer.from('b'), 0, 1), -1);
+assert.strictEqual(b.indexOf(Buffer.from('b'), 0, 2), 1);
+assert.strictEqual(b.includes('b', 0, 1), false);
+assert.strictEqual(b.includes('b', 0, 2), true);