diff --git a/lib/schemas/utils/socketServerImplementationPrototype.json b/lib/schemas/utils/socketServerImplementationPrototype.json
new file mode 100644
index 0000000000..a17dfe538c
--- /dev/null
+++ b/lib/schemas/utils/socketServerImplementationPrototype.json
@@ -0,0 +1,33 @@
+{
+  "type": "object",
+  "properties": {
+    "constructor": {
+      "instanceof": "Function"
+    },
+    "send": {
+      "instanceof": "Function"
+    },
+    "close": {
+      "instanceof": "Function"
+    },
+    "onConnection": {
+      "instanceof": "Function"
+    }
+  },
+  "errorMessage": {
+    "properties": {
+      "constructor": "- serverMode must have a constructor that takes a single server argument and calls super(server) on the superclass BaseServer, found via require('webpack-dev-server/lib/servers/BaseServer')",
+      "send": "- serverMode must have a send(connection, message) method that sends the message string to the provided client connection object",
+      "close": "- serverMode must have a close(connection) method that closes the provided client connection object",
+      "onConnection": "- serverMode must have a onConnection(f) method that calls f(connection) whenever a new client connection is made"
+    },
+    "required": {
+      "constructor": "- serverMode must have a constructor that takes a single server argument and calls super(server) on the superclass BaseServer, found via require('webpack-dev-server/lib/servers/BaseServer')",
+      "send": "- serverMode must have a send(connection, message) method that sends the message string to the provided client connection object",
+      "close": "- serverMode must have a close(connection) method that closes the provided client connection object",
+      "onConnection": "- serverMode must have a onConnection(f) method that calls f(connection) whenever a new client connection is made"
+    }
+  },
+  "required": ["constructor", "send", "close", "onConnection"],
+  "additionalProperties": true
+}
diff --git a/lib/utils/getSocketServerImplementation.js b/lib/utils/getSocketServerImplementation.js
index 6df634085f..f53f2af539 100644
--- a/lib/utils/getSocketServerImplementation.js
+++ b/lib/utils/getSocketServerImplementation.js
@@ -1,5 +1,8 @@
 'use strict';
 
+const validateOptions = require('schema-utils');
+const schema = require('../schemas/utils/socketServerImplementationPrototype.json');
+
 function getSocketServerImplementation(options) {
   let ServerImplementation;
   let serverImplFound = true;
@@ -35,6 +38,8 @@ function getSocketServerImplementation(options) {
     );
   }
 
+  validateOptions(schema, ServerImplementation.prototype, 'webpack Dev Server');
+
   return ServerImplementation;
 }
 
diff --git a/test/server/utils/__snapshots__/getSocketServerImplementation.test.js.snap b/test/server/utils/__snapshots__/getSocketServerImplementation.test.js.snap
new file mode 100644
index 0000000000..d67f1e59f6
--- /dev/null
+++ b/test/server/utils/__snapshots__/getSocketServerImplementation.test.js.snap
@@ -0,0 +1,37 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`getSocketServerImplementation util should throw with serverMode (bad path) 1`] = `[Error: serverMode must be a string denoting a default implementation (e.g. 'sockjs'), a full path to a JS file which exports a class extending BaseServer (webpack-dev-server/lib/servers/BaseServer) via require.resolve(...), or the class itself which extends BaseServer]`;
+
+exports[`getSocketServerImplementation util should throw with serverMode (no close, onConnection methods) 1`] = `
+[ValidationError: webpack Dev Server Invalid Options
+
+options - serverMode must have a close(connection) method that closes the provided client connection object
+options - serverMode must have a onConnection(f) method that calls f(connection) whenever a new client connection is made
+]
+`;
+
+exports[`getSocketServerImplementation util should throw with serverMode (no constructor, send, close, onConnection methods) 1`] = `
+[ValidationError: webpack Dev Server Invalid Options
+
+options [object Object]
+options - serverMode must have a send(connection, message) method that sends the message string to the provided client connection object
+options - serverMode must have a close(connection) method that closes the provided client connection object
+options - serverMode must have a onConnection(f) method that calls f(connection) whenever a new client connection is made
+]
+`;
+
+exports[`getSocketServerImplementation util should throw with serverMode (no onConnection method) 1`] = `
+[ValidationError: webpack Dev Server Invalid Options
+
+options - serverMode must have a onConnection(f) method that calls f(connection) whenever a new client connection is made
+]
+`;
+
+exports[`getSocketServerImplementation util should throw with serverMode (no send, close, onConnection methods) 1`] = `
+[ValidationError: webpack Dev Server Invalid Options
+
+options - serverMode must have a send(connection, message) method that sends the message string to the provided client connection object
+options - serverMode must have a close(connection) method that closes the provided client connection object
+options - serverMode must have a onConnection(f) method that calls f(connection) whenever a new client connection is made
+]
+`;
diff --git a/test/server/utils/getSocketServerImplementation.test.js b/test/server/utils/getSocketServerImplementation.test.js
index 0a157c39a9..50b7c5bd5c 100644
--- a/test/server/utils/getSocketServerImplementation.test.js
+++ b/test/server/utils/getSocketServerImplementation.test.js
@@ -1,10 +1,13 @@
 'use strict';
 
+/* eslint-disable constructor-super, no-empty-function, no-useless-constructor, no-unused-vars, class-methods-use-this */
+
 const getSocketServerImplementation = require('../../../lib/utils/getSocketServerImplementation');
+const BaseServer = require('../../../lib/servers/BaseServer');
 const SockJSServer = require('../../../lib/servers/SockJSServer');
 
 describe('getSocketServerImplementation util', () => {
-  it("should works with string serverMode ('sockjs')", () => {
+  it("should work with string serverMode ('sockjs')", () => {
     let result;
 
     expect(() => {
@@ -16,7 +19,7 @@ describe('getSocketServerImplementation util', () => {
     expect(result).toEqual(SockJSServer);
   });
 
-  it('should works with serverMode (SockJSServer class)', () => {
+  it('should work with serverMode (SockJSServer class)', () => {
     let result;
 
     expect(() => {
@@ -40,11 +43,90 @@ describe('getSocketServerImplementation util', () => {
     expect(result).toEqual(SockJSServer);
   });
 
-  it('should throws with serverMode (bad path)', () => {
+  it('should work with serverMode (additional class methods)', () => {
+    let result;
+
+    const ExtendedSockJSServer = class ExtendedSockJSServer extends SockJSServer {
+      myMethod() {
+        this.test = true;
+      }
+    };
+
     expect(() => {
-      getSocketServerImplementation({
-        serverMode: '/bad/path/to/implementation',
+      result = getSocketServerImplementation({
+        serverMode: ExtendedSockJSServer,
       });
-    }).toThrow(/serverMode must be a string/);
+    }).not.toThrow();
+
+    expect(result).toEqual(ExtendedSockJSServer);
+  });
+
+  const ClassWithoutConstructor = class ClassWithoutConstructor {};
+  // eslint-disable-next-line no-undefined
+  ClassWithoutConstructor.prototype.constructor = undefined;
+
+  const badSetups = [
+    {
+      title: 'should throw with serverMode (bad path)',
+      config: {
+        serverMode: '/bad/path/to/implementation',
+      },
+    },
+    {
+      title:
+        'should throw with serverMode (no constructor, send, close, onConnection methods)',
+      config: {
+        serverMode: ClassWithoutConstructor,
+      },
+    },
+    {
+      title:
+        'should throw with serverMode (no send, close, onConnection methods)',
+      config: {
+        serverMode: class ServerImplementation extends BaseServer {
+          constructor(server) {
+            super(server);
+          }
+        },
+      },
+    },
+    {
+      title: 'should throw with serverMode (no close, onConnection methods)',
+      config: {
+        serverMode: class ServerImplementation extends BaseServer {
+          constructor(server) {
+            super(server);
+          }
+
+          send(connection, message) {}
+        },
+      },
+    },
+    {
+      title: 'should throw with serverMode (no onConnection method)',
+      config: {
+        serverMode: class ServerImplementation extends BaseServer {
+          constructor(server) {
+            super(server);
+          }
+
+          send(connection, message) {}
+
+          close(connection) {}
+        },
+      },
+    },
+  ];
+
+  badSetups.forEach((setup) => {
+    it(setup.title, () => {
+      let thrown = false;
+      try {
+        getSocketServerImplementation(setup.config);
+      } catch (e) {
+        thrown = true;
+        expect(e).toMatchSnapshot();
+      }
+    });
   });
 });