gnome-terminal : small gap at right side of screen (Ubuntu)

I use gnome-terminal on Ubuntu, and when the window is small (not maximized or fullscreen), my tmux statusline and the ZSH right prompt both stretch to the extreme right of the window, which is perfect.

However, when maximized or fullscreen, there is a small but annoying gap at the right edge of the screen.

Is there any way this can be fixed?

(I know it's nearly insignificant; please be nice!)