diff --git a/moto/moto_server/werkzeug_app.py b/moto/moto_server/werkzeug_app.py
index 8d9c3bc77..107eae0b1 100644
--- a/moto/moto_server/werkzeug_app.py
+++ b/moto/moto_server/werkzeug_app.py
@@ -3,8 +3,16 @@ import os
 import os.path
 from threading import Lock
 
-from flask import Flask
-from flask_cors import CORS
+try:
+    from flask import Flask
+    from flask_cors import CORS
+except ImportError:
+    import warnings
+
+    warnings.warn(
+        "When using MotoServer, ensure that you install moto[server] to have all dependencies!\n"
+    )
+    raise
 
 import moto.backends as backends
 import moto.backend_index as backend_index
diff --git a/setup.py b/setup.py
index 11b9e9f22..0b201fb3c 100755
--- a/setup.py
+++ b/setup.py
@@ -39,8 +39,6 @@ install_requires = [
     "MarkupSafe!=2.0.0a1",  # This is a Jinja2 dependency, 2.0.0a1 currently seems broken
     "Jinja2>=2.10.1",
     "importlib_metadata ; python_version < '3.8'",
-    "flask<2.2.0",  # Required for the ThreadedMotoServer
-    "flask-cors"
 ]
 
 _dep_PyYAML = "PyYAML>=5.1"
@@ -75,7 +73,7 @@ all_extra_deps = [
     _dep_openapi,
     _setuptools,
 ]
-all_server_deps = all_extra_deps
+all_server_deps = all_extra_deps + ["flask<2.2.0", "flask-cors"]
 
 extras_per_service = {}
 for service_name in [