diff --git a/src/__tests__/reactive.spec.ts.ts b/src/__tests__/reactive.spec.ts
similarity index 97%
rename from src/__tests__/reactive.spec.ts.ts
rename to src/__tests__/reactive.spec.ts
index 4698815..072f551 100644
--- a/src/__tests__/reactive.spec.ts.ts
+++ b/src/__tests__/reactive.spec.ts
@@ -301,4 +301,11 @@ describe('reactive', () => {
     await nextTick()
     expect(callback.mock.calls[2][0]).toBe(500)
   })
+
+  it('should preserve argument count for splice', () => {
+    const data = reactive([1, 2, 3, 4, 5])
+    const tail = data.splice(2)
+    expect(data).toEqual([1, 2])
+    expect(tail).toEqual([3, 4, 5])
+  })
 })
diff --git a/src/reactive.ts b/src/reactive.ts
index 17cd166..e03a197 100644
--- a/src/reactive.ts
+++ b/src/reactive.ts
@@ -325,8 +325,14 @@ function arrayOperation(
     case 'fill':
       return (...args: any[]) => synthetic(...args.map((arg) => r(arg)))
     case 'splice':
-      return (start: number, remove?: number, ...inserts: any[]) =>
-        synthetic(start, remove, ...inserts.map((arg) => r(arg)))
+      return function (start: number, remove?: number, ...inserts: any[]) {
+        // Preserve the argument count when there's only one argument,
+        // because if a second argument is passed but undefined,
+        // it gets treated as 0.
+        return arguments.length === 1 ?
+          synthetic(start) :
+          synthetic(start, remove, ...inserts.map((arg) => r(arg)))
+      }
     default:
       return native
   }