Using SDL mouse deltas to make an FPS camera

I am using SDL’s relative mouse deltas to change the yaw and pitch of my 3D camera.
But there’s a problem when I use vsync. Since it blocks the main thread the next time I poll for the
mouse deltas they’ve been accumulating for some time and I get huge deltas.
This shouldn’t be a problem but for some reason it’s non-linear. The higher fps I have the lower
the mouse sensitivity feels and with low fps it jumps maany pixels per frame when constantly moving the mouse.

Show us the code that calculates the mouse delta and how you then apply the value(s) to your camera.