diff --git a/package.json b/package.json
index a2afadec3..1d956c24e 100644
--- a/package.json
+++ b/package.json
@@ -114,6 +114,7 @@
     "@vue/test-utils": "2.4.6",
     "axe-core": "4.11.1",
     "fast-check": "4.5.3",
+    "h3": "1.15.5",
     "knip": "5.83.0",
     "lint-staged": "16.2.7",
     "oxfmt": "0.27.0",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index c464f3f31..79d94fb3a 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -240,6 +240,9 @@ importers:
       fast-check:
         specifier: 4.5.3
         version: 4.5.3
+      h3:
+        specifier: 1.15.5
+        version: 1.15.5
       knip:
         specifier: 5.83.0
         version: 5.83.0(@types/node@24.10.9)(typescript@5.9.3)
diff --git a/test/unit/server/utils/error-handler.spec.ts b/test/unit/server/utils/error-handler.spec.ts
new file mode 100644
index 000000000..79024132f
--- /dev/null
+++ b/test/unit/server/utils/error-handler.spec.ts
@@ -0,0 +1,47 @@
+import { describe, expect, it } from 'vitest'
+import { createError } from 'h3'
+import * as v from 'valibot'
+import { handleApiError } from '../../../../server/utils/error-handler'
+
+describe('handleApiError', () => {
+  const fallback = { message: 'Something went wrong', statusCode: 500 }
+
+  it('re-throws H3 errors as-is', () => {
+    const h3Err = createError({ statusCode: 404, message: 'Not found' })
+
+    expect(() => handleApiError(h3Err, fallback)).toThrow(h3Err)
+  })
+
+  it('throws a 404 with the first issue message for valibot errors', () => {
+    const schema = v.object({ name: v.pipe(v.string(), v.minLength(1, 'Name is required')) })
+
+    let valibotError: unknown
+    try {
+      v.parse(schema, { name: '' })
+    } catch (e) {
+      valibotError = e
+    }
+
+    expect(() => handleApiError(valibotError, fallback)).toThrow(
+      expect.objectContaining({ statusCode: 404, message: 'Name is required' }),
+    )
+  })
+
+  it('throws a fallback error with the given statusCode and message', () => {
+    expect(() =>
+      handleApiError(new Error('unexpected'), { message: 'Bad gateway', statusCode: 502 }),
+    ).toThrow(expect.objectContaining({ statusCode: 502, message: 'Bad gateway' }))
+  })
+
+  it('defaults fallback statusCode to 502 when not provided', () => {
+    expect(() => handleApiError('some string error', { message: 'Upstream failed' })).toThrow(
+      expect.objectContaining({ statusCode: 502, message: 'Upstream failed' }),
+    )
+  })
+
+  it('uses the custom fallback statusCode when provided', () => {
+    expect(() => handleApiError(null, { message: 'Service unavailable', statusCode: 503 })).toThrow(
+      expect.objectContaining({ statusCode: 503, message: 'Service unavailable' }),
+    )
+  })
+})