diff --git a/source/cfdi-test.py b/source/cfdi-test.py
index d02bfbc..9b8e89c 100755
--- a/source/cfdi-test.py
+++ b/source/cfdi-test.py
@@ -10,10 +10,10 @@ def main(args):
         return
 
     if args.dir_trabajo:
-        entrada = util.join(args.dir_trabajo, 'entrada')
-        generados = util.join(args.dir_trabajo, 'generados')
-        por_timbrar = util.join(args.dir_trabajo, 'por_timbrar')
-        timbrados = util.join(args.dir_trabajo, 'timbrados')
+        entrada = util.validar_dir(args.dir_trabajo, 'entrada')
+        generados = util.validar_dir(args.dir_trabajo, 'generados')
+        por_timbrar = util.validar_dir(args.dir_trabajo, 'por_timbrar')
+        timbrados = util.validar_dir(args.dir_trabajo, 'timbrados')
     else:
         entrada = args.dir_entrada
         generados = args.dir_generados
diff --git a/source/util.py b/source/util.py
index 7560c01..31c3370 100644
--- a/source/util.py
+++ b/source/util.py
@@ -34,13 +34,20 @@ NS_CFDI = {
 }
 
 
+def validar_dir(base, name):
+    path = _join(base, name)
+    if not _exists(path):
+        os.makedirs(path)
+    return path
+
+
 def _exists(path):
     if not path:
         return False
     return Path(path).exists()
 
 
-def join(*paths):
+def _join(*paths):
     return str(Path(paths[0]).joinpath(*paths[1:]))
 
 
@@ -349,9 +356,9 @@ def _validate_args_validar_cert(args):
         log.error(msg)
         return False, data
 
-    path_cer = join(path_cert, f'{name}.cer')
-    path_key = join(path_cert, f'{name}.key')
-    path_enc = join(path_cert, f'{name}.enc')
+    path_cer = _join(path_cert, f'{name}.cer')
+    path_key = _join(path_cert, f'{name}.key')
+    path_enc = _join(path_cert, f'{name}.enc')
 
     if not _exists(path_cer):
         msg = f'No se encontró el archivo CER en: {path_cer}'
@@ -428,14 +435,14 @@ def make(source, target):
 
 def _stamp(path, target):
     current_path = os.path.dirname(__file__)
-    path_cer = join(current_path, 'certificados')
-    path_xslt = join(current_path, 'xslt', 'cadena.xslt')
+    path_cer = _join(current_path, 'certificados')
+    path_xslt = _join(current_path, 'xslt', 'cadena.xslt')
     doc = ET.parse(path)
 
     for pac in PACs.keys():
         xslt = open(path_xslt, 'rb')
-        cer = read_file(join(path_cer, f'{pac}.cer'))
-        key = read_file(join(path_cer, f'{pac}.enc'))
+        cer = read_file(_join(path_cer, f'{pac}.cer'))
+        key = read_file(_join(path_cer, f'{pac}.enc'))
         cert = SATCertificate(cer, key)
         # ~ print(cert)
 
@@ -512,17 +519,13 @@ def read_file(path):
     return data
 
 
-
-
 def get_files(path, ext='xml'):
     docs = []
     for folder, _, files in os.walk(path):
         pattern = re.compile('\.{}'.format(ext), re.IGNORECASE)
-        docs += [join(folder,f) for f in files if pattern.search(f)]
+        docs += [_join(folder,f) for f in files if pattern.search(f)]
     return tuple(docs)
 
 
-
-
 def _replace_ext(path, ext):
     return str(Path(path).with_suffix(ext))