diff --git a/client-src/default/utils/createSocketUrl.js b/client-src/default/utils/createSocketUrl.js
index d847769021..b7bf6c944d 100644
--- a/client-src/default/utils/createSocketUrl.js
+++ b/client-src/default/utils/createSocketUrl.js
@@ -16,8 +16,10 @@ function createSocketUrl(resourceQuery) {
     // Else, get the url from the <script> this file was called with.
     let scriptHost = getCurrentScriptSource();
 
-    // eslint-disable-next-line no-useless-escape
-    scriptHost = scriptHost.replace(/\/[^\/]+$/, '');
+    if (scriptHost) {
+      // eslint-disable-next-line no-useless-escape
+      scriptHost = scriptHost.replace(/\/[^\/]+$/, '');
+    }
     urlParts = url.parse(scriptHost || '/', false, true);
   }
 
diff --git a/test/client/utils/__snapshots__/createSocketUrl.test.js.snap b/test/client/utils/__snapshots__/createSocketUrl.test.js.snap
index cc455bf5ca..639b1588e2 100644
--- a/test/client/utils/__snapshots__/createSocketUrl.test.js.snap
+++ b/test/client/utils/__snapshots__/createSocketUrl.test.js.snap
@@ -16,6 +16,8 @@ exports[`createSocketUrl should return the url when __resourceQuery is https://e
 
 exports[`createSocketUrl should return the url when __resourceQuery is https://localhost:123 1`] = `"ttps:localhost:123/sockjs-node"`;
 
+exports[`createSocketUrl should return the url when __resourceQuery is undefined 1`] = `"/sockjs-node"`;
+
 exports[`createSocketUrl should return the url when the current script source is ?test 1`] = `"/sockjs-node"`;
 
 exports[`createSocketUrl should return the url when the current script source is http://0.0.0.0 1`] = `"http:/sockjs-node"`;
@@ -31,3 +33,5 @@ exports[`createSocketUrl should return the url when the current script source is
 exports[`createSocketUrl should return the url when the current script source is https://example.com/path/foo.js 1`] = `"https://example.com/sockjs-node"`;
 
 exports[`createSocketUrl should return the url when the current script source is https://localhost:123 1`] = `"https:/sockjs-node"`;
+
+exports[`createSocketUrl should return the url when the current script source is undefined 1`] = `"/sockjs-node"`;
diff --git a/test/client/utils/createSocketUrl.test.js b/test/client/utils/createSocketUrl.test.js
index 09a4cd6adc..e865ada8ee 100644
--- a/test/client/utils/createSocketUrl.test.js
+++ b/test/client/utils/createSocketUrl.test.js
@@ -13,6 +13,8 @@ describe('createSocketUrl', () => {
     // TODO: comment out after the major release
     // https://github.com/webpack/webpack-dev-server/pull/1954#issuecomment-498043376
     // 'file://filename',
+    // eslint-disable-next-line no-undefined
+    undefined,
   ];
 
   samples.forEach((url) => {