Error with database alias when running blastp

I have made a blast protein database with this command:

./makeblastdb -in input.fsa -out prot.db -dbtype prot -hash_index

It has generated 8 files as follows:

prot.db.phd  prot.db.phi  prot.db.phr  prot.db.pin  prot.db.pog  prot.db.psd  prot.db.psi  prot.db.psq

I have put everything in one folder called prot.db and now want to run the blastp with this command:

blastp -db  prot.db/ -query pep.fa -out results.out

But it gives me the following error which I don't understand how to solve:
BLAST Database error: No alias or index file found for protein database [prot.db/] in search path

I have been looking around to find a solution but I don't understand how I should proceed. Any help would be appreciated.