diff --git a/server/config.ts b/server/config.ts
index 3a73208c4..1e9ae55a2 100644
--- a/server/config.ts
+++ b/server/config.ts
@@ -59,17 +59,24 @@ function normalizeOrigins(raw: readonly string[]): string[] {
  *
  * Precedence:
  *   1. `PUBLIC_ORIGIN` — comma-separated list (platform domain + custom domain
- *      can coexist). Invalid entries are dropped.
+ *      can coexist). Invalid entries are dropped; a list that survives
+ *      normalization with at least one entry wins outright.
  *   2. Platform auto-detection — `RENDER_EXTERNAL_URL` (full URL) and/or
  *      `https://${RAILWAY_PUBLIC_DOMAIN}` (host only). Both are included when
  *      both env vars are present, keeping one-click deploys config-free.
+ *      Reached when `PUBLIC_ORIGIN` is unset *or* every entry in it is
+ *      unparseable, so a malformed value degrades to auto-detection rather
+ *      than suppressing it.
  *   3. `[]` — no public origin configured; the CSRF check falls back to the
  *      inbound `Host` header.
  */
 export function resolvePublicOrigins(env: Record<string, string | undefined>): string[] {
-  const explicit = readCsvList(env.PUBLIC_ORIGIN)
+  // Normalize before the precedence test, not after: gating on the raw CSV
+  // length lets an all-invalid PUBLIC_ORIGIN return [] while still claiming
+  // precedence, which suppresses platform auto-detection entirely.
+  const explicit = normalizeOrigins(readCsvList(env.PUBLIC_ORIGIN))
   if (explicit.length > 0) {
-    return normalizeOrigins(explicit)
+    return explicit
   }
 
   const derived: string[] = []
diff --git a/src/__tests__/server/serverConfig.test.ts b/src/__tests__/server/serverConfig.test.ts
index eab41dae1..fb467f4c8 100644
--- a/src/__tests__/server/serverConfig.test.ts
+++ b/src/__tests__/server/serverConfig.test.ts
@@ -85,6 +85,33 @@ describe('resolvePublicOrigins', () => {
     ).toEqual(['https://www.example.com'])
   })
 
+  it('falls back to platform vars when every PUBLIC_ORIGIN entry is invalid', () => {
+    // A one-click template that renders `https://${RAILWAY_PUBLIC_DOMAIN}`
+    // before the domain exists yields the bare scheme. Gating precedence on
+    // the raw CSV instead of the normalized result made that value suppress
+    // auto-detection, leaving the CSRF check with no configured origin — i.e.
+    // setting PUBLIC_ORIGIN badly was worse than not setting it at all.
+    expect(
+      resolvePublicOrigins({
+        PUBLIC_ORIGIN: 'https://',
+        RAILWAY_PUBLIC_DOMAIN: 'app.up.railway.app',
+      }),
+    ).toEqual(['https://app.up.railway.app'])
+  })
+
+  it('falls back to platform vars when PUBLIC_ORIGIN is only separators', () => {
+    expect(
+      resolvePublicOrigins({
+        PUBLIC_ORIGIN: 'not-a-url, also-bad',
+        RENDER_EXTERNAL_URL: 'https://app.onrender.com',
+      }),
+    ).toEqual(['https://app.onrender.com'])
+  })
+
+  it('returns [] when PUBLIC_ORIGIN is invalid and no platform var is set', () => {
+    expect(resolvePublicOrigins({ PUBLIC_ORIGIN: 'https://' })).toEqual([])
+  })
+
   it('returns [] when nothing is configured', () => {
     expect(resolvePublicOrigins({})).toEqual([])
   })