Zend certified PHP/Magento developer

Wrong sort order on category page Magento 2.3.0

I have created an attribute that is used for sorting on the category pages. The sorting order is numeric.
Expectation is that sorting order is:
1. 1
2. 2
3. 11

But the actual sort order is:
1. 1
2. 11
3. 2

Apparantly, Magento sorts on the first digit. Not on the complete integer.
How to effectuate the correct sort order?