diff --git a/server/cli/launch.py b/server/cli/launch.py
index 14e70000..8d2cf178 100644
--- a/server/cli/launch.py
+++ b/server/cli/launch.py
@@ -11,7 +11,7 @@ import click
 from server.app.app import Server
 from server.app.util.errors import ScanpyFileError
 from server.app.util.utils import custom_format_warning
-from server.utils.utils import find_available_port
+from server.utils.utils import find_available_port, is_port_available
 
 
 # anything bigger than this will generate a special message
@@ -141,7 +141,14 @@ security risk by including the --scripts flag. Make sure you trust the scripts t
         file_parts = splitext(basename(data))
         title = file_parts[0]
 
-    if not port:
+    if port:
+        if debug:
+            raise click.ClickException("--port and --debug may not be used together (try --verbose for error logging).")
+        if not is_port_available(host, int(port)):
+            raise click.ClickException(
+                f"The port selected {port} is in use, please specify an open port using the --port flag."
+            )
+    else:
         port = find_available_port(host)
 
     # Setup app
@@ -199,7 +206,7 @@ security risk by including the --scripts flag. Make sure you trust the scripts t
         sys.stdout = f
 
     try:
-        server.app.run(host=host, debug=debug, port=port, threaded=True)
+        server.app.run(host=host, debug=debug, port=port, threaded=True, use_debugger=False)
     except OSError as e:
         if e.errno == errno.EADDRINUSE:
             raise click.ClickException("Port is in use, please specify an open port using the --port flag.") from e
diff --git a/server/test/test_api.py b/server/test/test_api.py
index 24791879..7f396431 100644
--- a/server/test/test_api.py
+++ b/server/test/test_api.py
@@ -19,7 +19,7 @@ class EndPoints(unittest.TestCase):
 
     @classmethod
     def setUpClass(cls):
-        cls.ps = Popen(["cellxgene", "launch", "example-dataset/pbmc3k.h5ad", "--debug", "--port", "5005"])
+        cls.ps = Popen(["cellxgene", "launch", "example-dataset/pbmc3k.h5ad", "--verbose", "--port", "5005"])
         session = requests.Session()
         for i in range(90):
             try:
diff --git a/server/test/test_nan_rest.py b/server/test/test_nan_rest.py
index 23b3db50..a9ba4dd7 100644
--- a/server/test/test_nan_rest.py
+++ b/server/test/test_nan_rest.py
@@ -8,7 +8,7 @@ import decode_fbs
 
 import requests
 
-LOCAL_URL = "http://127.0.0.1:5005/"
+LOCAL_URL = "http://127.0.0.1:5006/"
 VERSION = "v0.2"
 URL_BASE = f"{LOCAL_URL}api/{VERSION}/"
 
@@ -21,7 +21,7 @@ class WithNaNs(unittest.TestCase):
     @classmethod
     def setUpClass(cls):
         cls.ps = Popen(
-            ["cellxgene", "launch", "server/test/test_datasets/nan.h5ad", "--debug", "--port", "5005"]
+            ["cellxgene", "launch", "server/test/test_datasets/nan.h5ad", "--verbose", "--port", "5006"]
         )
         session = requests.Session()
         for i in range(90):
diff --git a/server/utils/utils.py b/server/utils/utils.py
index 37a984e4..239f45bd 100644
--- a/server/utils/utils.py
+++ b/server/utils/utils.py
@@ -10,10 +10,17 @@ def find_available_port(host, port=5005):
     # Takes approx 2 seconds to do a scan of 5000 ports on my laptop
     num_ports_to_try = 5000
     for port_to_try in range(port, port + num_ports_to_try):
-        with contextlib.closing(socket.socket(socket.AF_INET, socket.SOCK_STREAM)) as s:
-            try:
-                s.bind((host, port_to_try))
-                return port_to_try
-            except socket.error:
-                pass
+        if is_port_available(host, port_to_try):
+            return port_to_try
     raise socket.error(errno.EADDRINUSE, f"No port in range {port} - {port + num_ports_to_try - 1} available.")
+
+
+def is_port_available(host, port):
+    is_available = False
+    with contextlib.closing(socket.socket(socket.AF_INET, socket.SOCK_STREAM)) as s:
+        try:
+            s.bind((host, port))
+            is_available = True
+        except socket.error:
+            pass
+    return is_available