diff --git a/types/node/inspector.d.ts b/types/node/inspector.d.ts
index 5f25a7d6bd..8abee3951f 100644
--- a/types/node/inspector.d.ts
+++ b/types/node/inspector.d.ts
@@ -3251,7 +3251,7 @@ declare module "inspector" {
     function close(): void;
 
     /**
-     * Return the URL of the active inspector, or undefined if there is none.
+     * Return the URL of the active inspector, or `undefined` if there is none.
      */
-    function url(): string;
+    function url(): string | undefined;
 }
diff --git a/types/node/node-tests.ts b/types/node/node-tests.ts
index 69981a7722..d5fe429815 100644
--- a/types/node/node-tests.ts
+++ b/types/node/node-tests.ts
@@ -1090,7 +1090,7 @@ import * as constants from 'constants';
         inspector.open(0, 'localhost');
         inspector.open(0, 'localhost', true);
         inspector.close();
-        const inspectorUrl: string = inspector.url();
+        const inspectorUrl: string | undefined = inspector.url();
 
         const session = new inspector.Session();
         session.connect();
diff --git a/types/node/scripts/generate-inspector/inspector.d.ts.template b/types/node/scripts/generate-inspector/inspector.d.ts.template
index a6715f12e4..5b6a02cbb2 100644
--- a/types/node/scripts/generate-inspector/inspector.d.ts.template
+++ b/types/node/scripts/generate-inspector/inspector.d.ts.template
@@ -73,7 +73,7 @@ declare module "inspector" {
     function close(): void;
 
     /**
-     * Return the URL of the active inspector, or undefined if there is none.
+     * Return the URL of the active inspector, or `undefined` if there is none.
      */
-    function url(): string;
+    function url(): string | undefined;
 }
diff --git a/types/node/v10/inspector.d.ts b/types/node/v10/inspector.d.ts
index 2dcd2760ad..9e1eea4b21 100644
--- a/types/node/v10/inspector.d.ts
+++ b/types/node/v10/inspector.d.ts
@@ -3156,7 +3156,7 @@ declare module "inspector" {
     function close(): void;
 
     /**
-     * Return the URL of the active inspector, or undefined if there is none.
+     * Return the URL of the active inspector, or `undefined` if there is none.
      */
-    function url(): string;
+    function url(): string | undefined;
 }
diff --git a/types/node/v10/node-tests.ts b/types/node/v10/node-tests.ts
index 22dab935f2..417689bc88 100644
--- a/types/node/v10/node-tests.ts
+++ b/types/node/v10/node-tests.ts
@@ -4822,7 +4822,7 @@ import * as constants from 'constants';
         inspector.open(0, 'localhost');
         inspector.open(0, 'localhost', true);
         inspector.close();
-        const inspectorUrl: string = inspector.url();
+        const inspectorUrl: string | undefined = inspector.url();
 
         const session = new inspector.Session();
         session.connect();
diff --git a/types/node/v11/inspector.d.ts b/types/node/v11/inspector.d.ts
index 5f25a7d6bd..8abee3951f 100644
--- a/types/node/v11/inspector.d.ts
+++ b/types/node/v11/inspector.d.ts
@@ -3251,7 +3251,7 @@ declare module "inspector" {
     function close(): void;
 
     /**
-     * Return the URL of the active inspector, or undefined if there is none.
+     * Return the URL of the active inspector, or `undefined` if there is none.
      */
-    function url(): string;
+    function url(): string | undefined;
 }
diff --git a/types/node/v11/node-tests.ts b/types/node/v11/node-tests.ts
index 69981a7722..d5fe429815 100644
--- a/types/node/v11/node-tests.ts
+++ b/types/node/v11/node-tests.ts
@@ -1090,7 +1090,7 @@ import * as constants from 'constants';
         inspector.open(0, 'localhost');
         inspector.open(0, 'localhost', true);
         inspector.close();
-        const inspectorUrl: string = inspector.url();
+        const inspectorUrl: string | undefined = inspector.url();
 
         const session = new inspector.Session();
         session.connect();
diff --git a/types/node/v8/inspector.d.ts b/types/node/v8/inspector.d.ts
index 19bba5af01..8deb30592c 100644
--- a/types/node/v8/inspector.d.ts
+++ b/types/node/v8/inspector.d.ts
@@ -2506,7 +2506,7 @@ declare module "inspector" {
     export function close(): void;
 
     /**
-     * Return the URL of the active inspector, or undefined if there is none.
+     * Return the URL of the active inspector, or `undefined` if there is none.
      */
-    export function url(): string;
+    export function url(): string | undefined;
 }
diff --git a/types/node/v8/node-tests.ts b/types/node/v8/node-tests.ts
index 27040c939d..a6b671550f 100644
--- a/types/node/v8/node-tests.ts
+++ b/types/node/v8/node-tests.ts
@@ -4041,7 +4041,7 @@ namespace inspector_tests {
         inspector.open(0, 'localhost');
         inspector.open(0, 'localhost', true);
         inspector.close();
-        const inspectorUrl: string = inspector.url();
+        const inspectorUrl: string | undefined = inspector.url();
 
         const session = new inspector.Session();
         session.connect();
diff --git a/types/node/v9/inspector.d.ts b/types/node/v9/inspector.d.ts
index 7088455c8c..b538c4108d 100644
--- a/types/node/v9/inspector.d.ts
+++ b/types/node/v9/inspector.d.ts
@@ -2524,7 +2524,7 @@ declare module "inspector" {
     export function close(): void;
 
     /**
-     * Return the URL of the active inspector, or undefined if there is none.
+     * Return the URL of the active inspector, or `undefined` if there is none.
      */
-    export function url(): string;
+    export function url(): string | undefined;
 }
diff --git a/types/node/v9/node-tests.ts b/types/node/v9/node-tests.ts
index d51d13d655..d3e55de398 100644
--- a/types/node/v9/node-tests.ts
+++ b/types/node/v9/node-tests.ts
@@ -4106,7 +4106,7 @@ namespace inspector_tests {
         inspector.open(0, 'localhost');
         inspector.open(0, 'localhost', true);
         inspector.close();
-        const inspectorUrl: string = inspector.url();
+        const inspectorUrl: string | undefined = inspector.url();
 
         const session = new inspector.Session();
         session.connect();