Manually setting the error on a bin

I am filling a histogram for display only, where I already know how many entries each bin has.
This is how I am filling it:

temp->Fill(min+ii*binwidth, y1);

where “min” is the lower limit of the x-axis, and ii goes from 0 to (number of bins -1);
y1 is the number of entries in each column (different at each iteration), which I already know, and here acts as a weight.
I calculate y1 somewhere else, and it has an error associated with it.

When I checked, it turns out that temp->GetBinError(some bin) and temp->GetBinContent(some bin) give the same answer, which makes the error bars huge.

I suspect this has to do with the fact that I am filling effectively only 1 entry per column.
Is there a way to get around this, such as setting the error on the bin by hand?

temp->SetBinError(min+ii*binwidth, some_error_value);