@@ -10,5 +10,19 @@ const Flex = ({ className, ...props }) => {
   return <Base {...props} flex className={cx} />
 }
 
+const responsivePropCheck = (props, propName, componentName) => {
+    if (typeof props[propName] === 'boolean') {
+      return new Error (
+        `Warning! The \`${propName}\` prop supplied to \`${componentName}\` now sets width instead of setting display flex. See https://github.com/jxnblk/reflexbox`
+      )
+    }
+}
+
+Flex.propTypes = {
+  sm: responsivePropCheck,
+  md: responsivePropCheck,
+  lg: responsivePropCheck
+}
+
 export default Flex
 