diff --git a/src/components/WikilinkChatInput.test.tsx b/src/components/WikilinkChatInput.test.tsx
index 1980a263..b31f2404 100644
--- a/src/components/WikilinkChatInput.test.tsx
+++ b/src/components/WikilinkChatInput.test.tsx
@@ -549,6 +549,7 @@ describe('WikilinkChatInput', () => {
   it('treats missing inputType as a non-insert beforeinput event', () => {
     expect(() => isInsertBeforeInput({} as InputEvent)).not.toThrow()
     expect(isInsertBeforeInput({} as InputEvent)).toBe(false)
+    expect(isInsertBeforeInput({ inputType: 42 })).toBe(false)
     expect(isInsertBeforeInput({ inputType: 'insertFromPaste' } as InputEvent)).toBe(true)
   })
 
@@ -567,6 +568,26 @@ describe('WikilinkChatInput', () => {
     expect(editor.textContent).toContain('still works')
   })
 
+  it('ignores beforeinput events with non-string inputType instead of calling startsWith', () => {
+    render(<Controlled />)
+
+    const editor = screen.getByTestId('agent-input')
+    const startsWith = vi.fn(() => true)
+    const beforeInputEvent = new Event('beforeinput', {
+      bubbles: true,
+      cancelable: true,
+    })
+    Object.defineProperty(beforeInputEvent, 'inputType', {
+      value: { startsWith },
+    })
+
+    expect(() => fireEvent(editor, beforeInputEvent)).not.toThrow()
+    expect(startsWith).not.toHaveBeenCalled()
+
+    updateEditorText('still works')
+    expect(editor.textContent).toContain('still works')
+  })
+
   it('recovers if unsupported media lands in the editor DOM', async () => {
     const onUnsupportedPaste = vi.fn()
     render(<Controlled onUnsupportedPaste={onUnsupportedPaste} />)
diff --git a/src/components/inlineWikilinkBeforeInput.ts b/src/components/inlineWikilinkBeforeInput.ts
index a9a6d39c..9c834287 100644
--- a/src/components/inlineWikilinkBeforeInput.ts
+++ b/src/components/inlineWikilinkBeforeInput.ts
@@ -1,11 +1,26 @@
-export function isInsertBeforeInput(nativeEvent: Pick<InputEvent, 'inputType'>) {
-  return typeof nativeEvent.inputType === 'string'
-    && nativeEvent.inputType.startsWith('insert')
+type BeforeInputLike = {
+  inputType?: unknown
+}
+
+type PlainTextBeforeInputLike = BeforeInputLike & {
+  data?: unknown
+  isComposing?: unknown
+}
+
+type PlainTextBeforeInput = PlainTextBeforeInputLike & {
+  data: string
+  inputType: 'insertText'
+  isComposing?: false
+}
+
+export function isInsertBeforeInput(nativeEvent: BeforeInputLike) {
+  const { inputType } = nativeEvent
+  return typeof inputType === 'string' && inputType.startsWith('insert')
 }
 
 export function isPlainTextBeforeInput(
-  nativeEvent: Pick<InputEvent, 'data' | 'inputType' | 'isComposing'>,
-): nativeEvent is Pick<InputEvent, 'inputType' | 'isComposing'> & { data: string } {
+  nativeEvent: PlainTextBeforeInputLike,
+): nativeEvent is PlainTextBeforeInput {
   return nativeEvent.inputType === 'insertText'
     && !nativeEvent.isComposing
     && typeof nativeEvent.data === 'string'