diff --git a/index.d.ts b/index.d.ts
index 7c929a4..7d48cef 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -14,7 +14,7 @@ export interface Props {
   onBlur?: (e: React.FocusEvent<HTMLInputElement>) => void,
   onChange?: (e: Event) => void,
   onClick?: (e: React.MouseEvent<HTMLInputElement>) => void,
-  tabIndex?: string | number,
+  tabIndex?: number,
   readOnly?: boolean,
   autoFocus?: boolean,
   value?: any,
diff --git a/src/Checkbox.jsx b/src/Checkbox.jsx
index 1d22293..df02aa0 100644
--- a/src/Checkbox.jsx
+++ b/src/Checkbox.jsx
@@ -18,7 +18,7 @@ class Checkbox extends Component {
     onBlur: PropTypes.func,
     onChange: PropTypes.func,
     onClick: PropTypes.func,
-    tabIndex: PropTypes.oneOfType([PropTypes.string, PropTypes.number]),
+    tabIndex: PropTypes.number,
     readOnly: PropTypes.bool,
     autoFocus: PropTypes.bool,
     value: PropTypes.any,