diff --git a/src/hooks/src/hooks/read-once-shared.ts b/src/hooks/src/hooks/read-once-shared.ts
index 6c0c6956..821ed0ef 100644
--- a/src/hooks/src/hooks/read-once-shared.ts
+++ b/src/hooks/src/hooks/read-once-shared.ts
@@ -64,11 +64,16 @@ export interface ReadOnceConfig {
   disabled: boolean;
 }
 
-export const getReadOnceConfig = (): ReadOnceConfig => ({
-  mode: process.env.READ_ONCE_MODE === 'deny' ? 'deny' : 'warn',
-  ttlMs: Math.max(1, parseInt(process.env.READ_ONCE_TTL ?? '', 10) || DEFAULT_TTL_MS / 1000) * 1000,
-  disabled: process.env.READ_ONCE_DISABLED === '1',
-});
+export const getReadOnceConfig = (): ReadOnceConfig => {
+  const ttlSecs = Number.isNaN(parseInt(process.env.READ_ONCE_TTL ?? '', 10))
+    ? DEFAULT_TTL_MS / 1000
+    : parseInt(process.env.READ_ONCE_TTL ?? '', 10);
+  return {
+    mode: process.env.READ_ONCE_MODE === 'deny' ? 'deny' : 'warn',
+    ttlMs: Math.max(1, ttlSecs) * 1000,
+    disabled: process.env.READ_ONCE_DISABLED === '1',
+  };
+};
 
 export const isFullRead = (ctx: HookContext): boolean =>
   !('offset' in ctx.toolInput) && !('limit' in ctx.toolInput);
diff --git a/src/hooks/tests/read-once.test.ts b/src/hooks/tests/read-once.test.ts
index 916845d5..7f9c77b4 100644
--- a/src/hooks/tests/read-once.test.ts
+++ b/src/hooks/tests/read-once.test.ts
@@ -36,7 +36,11 @@ vi.mock('../src/runtime/state-store', () => ({
 import { runHook } from '../src/runtime/run-hook';
 import { readOnceHook } from '../src/hooks/read-once';
 import { readOnceResetHook } from '../src/hooks/read-once-reset';
-import { readReadOnceState, READ_ONCE_NAMESPACE } from '../src/hooks/read-once-shared';
+import {
+  getReadOnceConfig,
+  readReadOnceState,
+  READ_ONCE_NAMESPACE,
+} from '../src/hooks/read-once-shared';
 
 const makeClaudeRead = (
   filePath: string,
@@ -172,6 +176,16 @@ describe('read-once', () => {
     expect(result).toBeNull();
   });
 
+  test('zero TTL is honoured as the floored minimum, not the default', () => {
+    process.env.READ_ONCE_TTL = '0';
+    expect(getReadOnceConfig().ttlMs).toBe(1000);
+  });
+
+  test('missing TTL falls back to the default', () => {
+    delete process.env.READ_ONCE_TTL;
+    expect(getReadOnceConfig().ttlMs).toBe(20 * 60 * 1000);
+  });
+
   test('preCompact reset clears the ledger for the current session', async () => {
     await runHookWithRaw(readOnceHook, makeClaudeRead(filePath));
     await runHookWithRaw(readOnceResetHook, makeClaudePreCompact('claude-session-001'));