How to undo a "git update-index --assume-unchanged" on a directory. "--no-assume-unchanged" does not work

Question

I have used

git update-index --assume-unchanged [directory name]

and expected that

git update-index --no-assume-unchanged [directory name]

would undo that command. However, it says "Ignoring path [directory name]" and the directly continues to be ignored.

I have also tried

git update-index --really-refresh --no-assume-unchanged [directory name]

but that did not work either.

I have tried doing

git update-index --no-assume-unchanged [file]

for each file inside the directory, but the directory is still being ignored.

I am using git version 1.8.4.mysysgit.0

Is there another way to make git stop ignoring a directory?