diff --git a/packages/dev-middleware/src/__tests__/InspectorProxyCdpTransport-test.js b/packages/dev-middleware/src/__tests__/InspectorProxyCdpTransport-test.js
index 5c3536be64a..5e2396edb0f 100644
--- a/packages/dev-middleware/src/__tests__/InspectorProxyCdpTransport-test.js
+++ b/packages/dev-middleware/src/__tests__/InspectorProxyCdpTransport-test.js
@@ -268,5 +268,123 @@ describe.each(['HTTP', 'HTTPS'])(
         debugger2?.close();
       }
     });
+
+    test('debugger connection to a nonexistent page is rejected', async () => {
+      let device, debugger_;
+      try {
+        device = await createDeviceMock(
+          `${serverRef.serverBaseWsUrl}/inspector/device?device=device1&name=foo&app=bar`,
+          autoCleanup.signal,
+        );
+        // Set up a page.
+        device.getPages.mockImplementation(() => [
+          {
+            app: 'bar-app',
+            id: 'page1',
+            title: 'bar-title',
+            vm: 'bar-vm',
+          },
+        ]);
+        let pageList: Array<PageDescription> = [];
+        await until(async () => {
+          pageList = (await fetchJson(
+            `${serverRef.serverBaseUrl}/json`,
+            // $FlowIgnore[unclear-type]
+          ): any);
+          expect(pageList).toHaveLength(1);
+        });
+        const [{webSocketDebuggerUrl}] = pageList;
+
+        // Connect the debugger to a nonexistent page.
+        debugger_ = await createDebuggerMock(
+          webSocketDebuggerUrl.replaceAll('page1', 'some-other-id'),
+          autoCleanup.signal,
+        );
+
+        // The debugger gets disconnected automatically.
+        await until(async () => {
+          expect([
+            // CLOSING
+            3,
+            // CLOSED
+            4,
+          ]).toContain(debugger_.socket.readyState);
+        });
+
+        expect(device.connect).not.toHaveBeenCalled();
+        expect(device.disconnect).not.toHaveBeenCalled();
+      } finally {
+        device?.close();
+        debugger_?.close();
+      }
+    });
+
+    test('debugger connection to a nonexistent page does not kill the current debugger connection', async () => {
+      let device, debugger1, debugger2;
+      try {
+        device = await createDeviceMock(
+          `${serverRef.serverBaseWsUrl}/inspector/device?device=device1&name=foo&app=bar`,
+          autoCleanup.signal,
+        );
+        // Set up a page.
+        device.getPages.mockImplementation(() => [
+          {
+            app: 'bar-app',
+            id: 'page1',
+            title: 'bar-title',
+            vm: 'bar-vm',
+          },
+        ]);
+        let pageList: Array<PageDescription> = [];
+        await until(async () => {
+          pageList = (await fetchJson(
+            `${serverRef.serverBaseUrl}/json`,
+            // $FlowIgnore[unclear-type]
+          ): any);
+          expect(pageList).toHaveLength(1);
+        });
+        const [{webSocketDebuggerUrl}] = pageList;
+
+        // Connect the first debugger.
+        debugger1 = await createDebuggerMock(
+          webSocketDebuggerUrl,
+          autoCleanup.signal,
+        );
+
+        // Connect a second debugger to a nonexistent page.
+        debugger2 = await createDebuggerMock(
+          webSocketDebuggerUrl.replaceAll('page1', 'some-other-id'),
+          autoCleanup.signal,
+        );
+
+        // The second debugger gets disconnected automatically.
+        await until(async () => {
+          expect([
+            // CLOSING
+            3,
+            // CLOSED
+            4,
+          ]).toContain(debugger2.socket.readyState);
+        });
+
+        // We can still send messages through the first debugger.
+        await sendFromDebuggerToTarget(debugger1, device, 'page1', {
+          method: 'Runtime.enable',
+          id: 0,
+        });
+
+        expect(device.connect).toHaveBeenCalledWith({
+          event: 'connect',
+          payload: {
+            pageId: 'page1',
+          },
+        });
+        expect(device.disconnect).not.toHaveBeenCalled();
+      } finally {
+        device?.close();
+        debugger1?.close();
+        debugger2?.close();
+      }
+    });
   },
 );
diff --git a/packages/dev-middleware/src/inspector-proxy/Device.js b/packages/dev-middleware/src/inspector-proxy/Device.js
index 7be749d07cd..4d058de8dd2 100644
--- a/packages/dev-middleware/src/inspector-proxy/Device.js
+++ b/packages/dev-middleware/src/inspector-proxy/Device.js
@@ -308,17 +308,30 @@ export default class Device {
       userAgent: string | null,
     }>,
   ) {
+    const page: ?Page =
+      pageId === REACT_NATIVE_RELOADABLE_PAGE_ID
+        ? this.#createSyntheticPage()
+        : this.#pages.get(pageId);
+
+    if (!page) {
+      debug(
+        `Got new debugger connection for page ${pageId} of ${this.#name}, but no such page exists`,
+      );
+      socket.close();
+      return;
+    }
+
     // Clear any commands we were waiting on.
     this.#deviceEventReporter?.logDisconnection('debugger');
 
+    // Disconnect current debugger if we already have debugger connected.
+    this.#terminateDebuggerConnection();
+
     this.#deviceEventReporter?.logConnection('debugger', {
       pageId,
       frontendUserAgent: metadata.userAgent,
     });
 
-    // Disconnect current debugger if we already have debugger connected.
-    this.#terminateDebuggerConnection();
-
     const debuggerInfo = {
       socket,
       prependedFilePrefix: false,
@@ -327,18 +340,11 @@ export default class Device {
       customHandler: null,
     };
 
-    // TODO(moti): Handle null case explicitly, e.g. refuse to connect to
-    // unknown pages.
-    const page: ?Page =
-      pageId === REACT_NATIVE_RELOADABLE_PAGE_ID
-        ? this.#createSyntheticPage()
-        : this.#pages.get(pageId);
-
     this.#debuggerConnection = debuggerInfo;
 
     debug(`Got new debugger connection for page ${pageId} of ${this.#name}`);
 
-    if (page && this.#debuggerConnection && this.#createCustomMessageHandler) {
+    if (this.#debuggerConnection && this.#createCustomMessageHandler) {
       this.#debuggerConnection.customHandler = this.#createCustomMessageHandler(
         {
           page,
@@ -405,7 +411,7 @@ export default class Device {
         return;
       }
 
-      if (!page || !this.#pageHasCapability(page, 'nativeSourceCodeFetching')) {
+      if (!this.#pageHasCapability(page, 'nativeSourceCodeFetching')) {
         processedReq = this.#interceptClientMessageForSourceFetching(
           debuggerRequest,
           debuggerInfo,