diff --git a/detector.py b/detector.py
index c95d25a..49c084b 100644
--- a/detector.py
+++ b/detector.py
@@ -41,7 +41,7 @@ def cli():
 
 
 @cli.command()
-@click.argument('path', type=click.Path())
+@click.argument('path', type=click.Path(exists=True))
 @click.argument('db', type=click.Path())
 def build(path, db):
     """
@@ -61,7 +61,7 @@ def build(path, db):
 
     # find fasta files and concatenate them to a temporary file
     with open(full_fasta, 'w') as f_out:
-        for file in path:
+        for file in os.listdir(path):
             if file.lower().endswith('.fasta'):
                 click.echo("\tFound file: %s" % file)
                 fasta_count += 1