diff --git a/src/utils/modifiers.test.ts b/src/utils/modifiers.test.ts
new file mode 100644
index 0000000..b17f783
--- /dev/null
+++ b/src/utils/modifiers.test.ts
@@ -0,0 +1,61 @@
+import { afterEach, beforeEach, describe, expect, mock, test } from 'bun:test'
+import { platform } from 'os'
+
+const isDarwin = platform() === 'darwin'
+
+describe('modifiers — modifiers-napi stub fail-closed', () => {
+  let originalPlatform:PropertyDescriptor | undefined
+  let requireMock: ReturnType<typeof mock>
+
+  beforeEach(() => {
+    // Stub require('modifiers-napi') to return the reservation-stub shape
+    // (no exports) that's published on public npm as modifiers-napi@0.0.1.
+    requireMock = mock((moduleName: string) => {
+      if (moduleName !== 'modifiers-napi') {
+        throw new Error(`unexpected require: ${moduleName}`)
+      }
+      return {} as { isModifierPressed?: (m: string) => boolean }
+    })
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    ;(globalThis as any).require = requireMock
+  })
+
+  afterEach(() => {
+    mock.restore()
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    delete (globalThis as any).require
+  })
+
+  test('isModifierPressed returns false instead of throwing when the native export is missing', async () => {
+    const originalPlatformDesc = Object.getOwnPropertyDescriptor(process, 'platform')
+    if (!isDarwin) {
+      Object.defineProperty(process, 'platform', { value: 'darwin', configurable: true })
+    }
+    try {
+      const { isModifierPressed } = await import('./modifiers.js')
+      // Must not throw TypeError. Stub has no isModifierPressed export, so the
+      // guard path runs and yields false (modifier reported as not pressed).
+      expect(() => isModifierPressed('shift')).not.toThrow()
+      expect(isModifierPressed('shift')).toBe(false)
+      expect(isModifierPressed('command')).toBe(false)
+    } finally {
+      if (originalPlatformDesc) {
+        Object.defineProperty(process, 'platform', originalPlatformDesc)
+      }
+    }
+  })
+
+  test('isModifierPressed returns false on non-darwin platforms regardless of stub', async () => {
+    Object.defineProperty(process, 'platform', { value: 'linux', configurable: true })
+    try {
+      const { isModifierPressed } = await import('./modifiers.js')
+      expect(isModifierPressed('shift')).toBe(false)
+      // The stub require() must not have been consulted on non-darwin.
+      expect(requireMock).toHaveBeenCalledTimes(0)
+    } finally {
+      if (originalPlatform) {
+        Object.defineProperty(process, 'platform', originalPlatform)
+      }
+    }
+  })
+})
\ No newline at end of file
diff --git a/src/utils/modifiers.ts b/src/utils/modifiers.ts
index 08bde4b..6f5579a 100644
--- a/src/utils/modifiers.ts
+++ b/src/utils/modifiers.ts
@@ -23,14 +23,24 @@ export function prewarmModifiers(): void {
 
 /**
  * Check if a specific modifier key is currently pressed (synchronous).
+ *
+ * `modifiers-napi` is a reserved stub (`0.0.1`, no exports) on public npm. When
+ * the native module is unavailable we fail closed: report the modifier as not
+ * pressed. That disables Apple_Terminal's best-effort Shift+Enter newline
+ * detection (a nicety) without breaking Enter submit (which the stub otherwise
+ * crashes on every keystroke).
  */
 export function isModifierPressed(modifier: ModifierKey): boolean {
   if (process.platform !== 'darwin') {
     return false
   }
-  // Dynamic import to avoid loading native module at top level
   const { isModifierPressed: nativeIsModifierPressed } =
     // eslint-disable-next-line @typescript-eslint/no-require-imports
-    require('modifiers-napi') as { isModifierPressed: (m: string) => boolean }
+    require('modifiers-napi') as {
+      isModifierPressed?: (m: string) => boolean
+    }
+  if (typeof nativeIsModifierPressed !== 'function') {
+    return false
+  }
   return nativeIsModifierPressed(modifier)
 }