bedtools2: Non-writable IO device error when intersecting BAM and BED files

I have a sorted BAM file that I want to filter for reads not overlapping regions in a BED file. However, the following error occurs:

bedtools intersect -a sample.bam -b regions.bed -v > reads.not.in.regions.bam
terminate called after throwing an instance of 'std::runtime_error'
  what():  BgzfStream::Write() - trying to write to non-writable IO device

I have plenty of space to write the files, and if I do not specify an output file it prints to the console.