diff --git a/apps/web/hooks/__tests__/use-sse.test.ts b/apps/web/hooks/__tests__/use-sse.test.ts
index d373b08..582bbb8 100644
--- a/apps/web/hooks/__tests__/use-sse.test.ts
+++ b/apps/web/hooks/__tests__/use-sse.test.ts
@@ -156,3 +156,30 @@ describe('useSSE hook', () => {
     vi.useRealTimers()
   })
 })
+
+describe('useSSE with relative NEXT_PUBLIC_API_URL', () => {
+  beforeEach(() => {
+    MockEventSource.reset()
+    vi.stubGlobal('EventSource', MockEventSource)
+  })
+
+  afterEach(() => {
+    vi.unstubAllGlobals()
+    vi.unstubAllEnvs()
+    vi.resetModules()
+  })
+
+  // Regression for issue #46: deployments behind nginx set NEXT_PUBLIC_API_URL
+  // to a relative path like "/api". `new URL("/api/events/abc")` throws
+  // "Failed to construct 'URL': Invalid URL" without a base, crashing the
+  // dashboard the moment UploadSSEBridge first opens an SSE connection.
+  it('builds a valid URL when NEXT_PUBLIC_API_URL is a relative path', async () => {
+    vi.stubEnv('NEXT_PUBLIC_API_URL', '/api')
+    vi.resetModules()
+    const { useSSE: useSSEFresh } = await import('../use-sse')
+
+    expect(() => renderHook(() => useSSEFresh('project-123'))).not.toThrow()
+    expect(MockEventSource.instances).toHaveLength(1)
+    expect(MockEventSource.instances[0].url).toContain('/api/events/project-123')
+  })
+})
diff --git a/apps/web/hooks/use-sse.ts b/apps/web/hooks/use-sse.ts
index c52c288..affb0db 100644
--- a/apps/web/hooks/use-sse.ts
+++ b/apps/web/hooks/use-sse.ts
@@ -126,7 +126,11 @@ export function useSSE(projectId: string | null | undefined, options: UseSSEOpti
       if (destroyed) return
 
       const token = getAccessToken()
-      const url = new URL(`${API_URL}/events/${projectId}`)
+      // Use window.location.origin as a base so deployments behind a reverse
+      // proxy can set NEXT_PUBLIC_API_URL to a relative path like "/api"
+      // without crashing the URL constructor.
+      const base = typeof window !== 'undefined' ? window.location.origin : 'http://localhost'
+      const url = new URL(`${API_URL}/events/${projectId}`, base)
       if (token) {
         url.searchParams.set('token', token)
       }