diff --git a/src/web-server/usage/profile-filter.ts b/src/web-server/usage/profile-filter.ts
index a319daa1..c3d0f2fd 100644
--- a/src/web-server/usage/profile-filter.ts
+++ b/src/web-server/usage/profile-filter.ts
@@ -9,8 +9,13 @@ export interface ProfileScopedUsageData {
 
 const PROFILE_NAME_REGEX = /^[A-Za-z0-9._-]+$/;
 
-export function normalizeProfileQuery(profile?: string): string | undefined {
-  const value = profile?.trim();
+export function normalizeProfileQuery(profile?: unknown): string | undefined {
+  if (profile === undefined) return undefined;
+  if (typeof profile !== 'string') {
+    throw new Error('Invalid profile filter');
+  }
+
+  const value = profile.trim();
   if (!value || value === 'all') return undefined;
   if (!PROFILE_NAME_REGEX.test(value)) {
     throw new Error('Invalid profile filter');
diff --git a/tests/unit/web-server/usage-handlers-semantics.test.ts b/tests/unit/web-server/usage-handlers-semantics.test.ts
index e91aec59..dfb1de23 100644
--- a/tests/unit/web-server/usage-handlers-semantics.test.ts
+++ b/tests/unit/web-server/usage-handlers-semantics.test.ts
@@ -83,11 +83,7 @@ function writeAssistantEntriesToDir(baseClaudeDir: string, entries: AssistantFix
       },
     });
 
-    fs.writeFileSync(
-      path.join(projectDir, `${entry.sessionId}.jsonl`),
-      `${line}\n`,
-      'utf-8'
-    );
+    fs.writeFileSync(path.join(projectDir, `${entry.sessionId}.jsonl`), `${line}\n`, 'utf-8');
   }
 }
 
@@ -222,7 +218,10 @@ describe('usage handlers semantics', () => {
       res as never
     );
 
-    const payload = res.payload as { success: boolean; data: Array<{ hour: string; requests: number }> };
+    const payload = res.payload as {
+      success: boolean;
+      data: Array<{ hour: string; requests: number }>;
+    };
     const targetHour = payload.data.find((row) => row.hour === '2026-03-02 10:00');
 
     expect(targetHour?.requests).toBe(3);
@@ -415,6 +414,19 @@ describe('usage handlers semantics', () => {
     });
   });
 
+  it('rejects non-string profile filters as validation errors', async () => {
+    for (const profile of [['work', 'default'], { name: 'work' }]) {
+      const res = createMockResponse();
+      await handlers.handleSummary({ query: { profile } } as never, res as never);
+
+      expect(res.statusCode).toBe(400);
+      expect(res.payload).toMatchObject({
+        success: false,
+        error: 'Invalid profile filter',
+      });
+    }
+  });
+
   it('rejects reversed date ranges before computing summary totals', async () => {
     const res = createMockResponse();