diff --git a/apps/server/src/routes/github/index.ts b/apps/server/src/routes/github/index.ts
index 798deae5..e8088159 100644
--- a/apps/server/src/routes/github/index.ts
+++ b/apps/server/src/routes/github/index.ts
@@ -45,7 +45,7 @@ export function createGitHubRoutes(events: EventEmitter): Router {
   router.post(
     '/validation-mark-viewed',
     validatePathParams('projectPath'),
-    createMarkViewedHandler()
+    createMarkViewedHandler(events)
   );
 
   return router;
diff --git a/apps/server/src/routes/github/routes/validation-endpoints.ts b/apps/server/src/routes/github/routes/validation-endpoints.ts
index 652aa3d2..21859737 100644
--- a/apps/server/src/routes/github/routes/validation-endpoints.ts
+++ b/apps/server/src/routes/github/routes/validation-endpoints.ts
@@ -3,6 +3,8 @@
  */
 
 import type { Request, Response } from 'express';
+import type { EventEmitter } from '../../../lib/events.js';
+import type { IssueValidationEvent } from '@automaker/types';
 import {
   isValidationRunning,
   getValidationStatus,
@@ -193,7 +195,7 @@ export function createDeleteValidationHandler() {
 /**
  * POST /validation-mark-viewed - Mark a validation as viewed by the user
  */
-export function createMarkViewedHandler() {
+export function createMarkViewedHandler(events: EventEmitter) {
   return async (req: Request, res: Response): Promise<void> => {
     try {
       const { projectPath, issueNumber } = req.body as {
@@ -215,6 +217,16 @@ export function createMarkViewedHandler() {
 
       const success = await markValidationViewed(projectPath, issueNumber);
 
+      if (success) {
+        // Emit event so UI can update the unviewed count
+        const viewedEvent: IssueValidationEvent = {
+          type: 'issue_validation_viewed',
+          issueNumber,
+          projectPath,
+        };
+        events.emit('issue-validation:event', viewedEvent);
+      }
+
       res.json({ success });
     } catch (error) {
       logError(error, 'Mark validation viewed failed');
diff --git a/apps/ui/src/components/layout/sidebar/hooks/use-unviewed-validations.ts b/apps/ui/src/components/layout/sidebar/hooks/use-unviewed-validations.ts
index 44470e3c..102b1fc9 100644
--- a/apps/ui/src/components/layout/sidebar/hooks/use-unviewed-validations.ts
+++ b/apps/ui/src/components/layout/sidebar/hooks/use-unviewed-validations.ts
@@ -45,7 +45,11 @@ export function useUnviewedValidations(currentProject: Project | null) {
       const unsubscribe = api.github.onValidationEvent((event) => {
         if (event.projectPath === currentProject.path) {
           if (event.type === 'issue_validation_complete') {
+            // New validation completed - increment count
             setCount((prev) => prev + 1);
+          } else if (event.type === 'issue_validation_viewed') {
+            // Validation was viewed - decrement count
+            setCount((prev) => Math.max(0, prev - 1));
           }
         }
       });
diff --git a/libs/types/src/issue-validation.ts b/libs/types/src/issue-validation.ts
index 84079907..2c0d2f64 100644
--- a/libs/types/src/issue-validation.ts
+++ b/libs/types/src/issue-validation.ts
@@ -109,6 +109,11 @@ export type IssueValidationEvent =
       issueNumber: number;
       error: string;
       projectPath: string;
+    }
+  | {
+      type: 'issue_validation_viewed';
+      issueNumber: number;
+      projectPath: string;
     };
 
 /**