Changing brush size with shortcut [ and ] - Photoshop

When I'm trying to change my brush size using the shortcut [ and ], it works fine when the size is 1px to 10px, but only increases/decreases in increments of 5 pixels instead of 1 pixel after that. (eg. When I want to increase my brush size from 10px to 13px, the ] key won't let me, because it would jump straight to 15px.) How can I fix this?

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