diff --git a/sapphire/__main__.py b/sapphire/__main__.py
index ab6d5f89..81999500 100644
--- a/sapphire/__main__.py
+++ b/sapphire/__main__.py
@@ -30,7 +30,7 @@ def parse_args(argv=None):
         help="Configure console logging (default: %(default)s)",
     )
     parser.add_argument(
-        "--port", type=int, help="Specify a port to bind to (default: random)"
+        "--port", default=0, type=int, help="Specify port (default: automatic)"
     )
     parser.add_argument(
         "--remote",
@@ -46,7 +46,9 @@ def parse_args(argv=None):
     args = parser.parse_args(argv)
     # sanity check
     if not args.path.is_dir():
-        parser.error(f"Path does not exist '{args.path}'")
+        parser.error(f"Directory does not exist '{args.path}'")
+    if args.port < 0 or args.port > 65535:
+        parser.error("--port must be >= 0 and <= 65535")
     if args.timeout < 0:
         parser.error("--timeout must be >= 0")
     args.log_level = level_map[args.log_level]
diff --git a/sapphire/core.py b/sapphire/core.py
index 83d1eaf0..c6f51af5 100644
--- a/sapphire/core.py
+++ b/sapphire/core.py
@@ -49,7 +49,7 @@
 
 def create_listening_socket(attempts=10, port=0, remote=False, timeout=None):
     """Create listening socket. Search for an open socket if needed and
-    and configure the socket. If a specific port is unavailable or no
+    configure the socket. If a specific port is unavailable or no
     available ports can be found socket.error will be raised.
 
     Args:
@@ -62,7 +62,7 @@ def create_listening_socket(attempts=10, port=0, remote=False, timeout=None):
         socket: A listening socket.
     """
     assert attempts > 0
-    assert port >= 0
+    assert 0 <= port <= 65535
     assert timeout is None or timeout > 0
 
     for remaining in reversed(range(attempts)):