Plotting boxes in gnuplot

When I plot a set of data in gnuplot from a file like:

1  5
2  3
4  6
5  1

using

plot "file.txt" w boxes

I would expect that at the x value of 3 it will go to a value of 0 for y... but it doesn't. Is there a way to fix that, or do I actually have to type by hand an additional line in my file:
3 0
This becomes very hard when I have a lot of points missing.

Hi.

Adding:

set boxwidth 1.0

seemed to omit the artifact you were talking about.

Best wishes ... cheers, drl