diff --git a/.gitignore b/.gitignore
index 64dcbce9b7f..c2f46f18bfe 100644
--- a/.gitignore
+++ b/.gitignore
@@ -53,3 +53,4 @@ virtualenv.py
 .python-version
 .pytest_cache
 .vscode
+.mypy_cache
\ No newline at end of file
diff --git a/CHANGES/2966.feature b/CHANGES/2966.feature
new file mode 100644
index 00000000000..2eed6c5c68c
--- /dev/null
+++ b/CHANGES/2966.feature
@@ -0,0 +1 @@
+Apply assertions in debug mode only
\ No newline at end of file
diff --git a/aiohttp/web_app.py b/aiohttp/web_app.py
index bebad310bdc..a808b06f917 100644
--- a/aiohttp/web_app.py
+++ b/aiohttp/web_app.py
@@ -309,11 +309,13 @@ def _prepare_middleware(self):
 
     async def _handle(self, request):
         match_info = await self._router.resolve(request)
-        assert isinstance(match_info, AbstractMatchInfo), match_info
+        if DEBUG:  # pragma: no cover
+            if not isinstance(match_info, AbstractMatchInfo):
+                raise TypeError("match_info should be AbstractMAtchInfo "
+                                "instance, not {!r}".format(match_info))
         match_info.add_app(self)
 
-        if __debug__:
-            match_info.freeze()
+        match_info.freeze()
 
         resp = None
         request._match_info = match_info
@@ -335,13 +337,15 @@ async def _handle(self, request):
 
             resp = await handler(request)
 
-        assert isinstance(resp, StreamResponse), \
-            ("Handler {!r} should return response instance, "
-             "got {!r} [middlewares {!r}]").format(
-                 match_info.handler, type(resp),
-                 [middleware
-                  for app in match_info.apps
-                  for middleware in app.middlewares])
+        if DEBUG:
+            if not isinstance(resp, StreamResponse):
+                msg = ("Handler {!r} should return response instance, "
+                       "got {!r} [middlewares {!r}]").format(
+                           match_info.handler, type(resp),
+                           [middleware
+                            for app in match_info.apps
+                            for middleware in app.middlewares])
+                raise TypeError(msg)
         return resp
 
     def __call__(self):
diff --git a/aiohttp/web_urldispatcher.py b/aiohttp/web_urldispatcher.py
index b0c327b1dc0..16cf008986d 100644
--- a/aiohttp/web_urldispatcher.py
+++ b/aiohttp/web_urldispatcher.py
@@ -18,6 +18,7 @@
 
 from . import hdrs
 from .abc import AbstractMatchInfo, AbstractRouter, AbstractView
+from .helpers import DEBUG
 from .http import HttpVersion11
 from .web_exceptions import (HTTPExpectationFailed, HTTPForbidden,
                              HTTPMethodNotAllowed, HTTPNotFound)
@@ -191,9 +192,11 @@ def current_app(self):
 
     @contextmanager
     def set_current_app(self, app):
-        assert app in self._apps, (
-            "Expected one of the following apps {!r}, got {!r}"
-            .format(self._apps, app))
+        if DEBUG:  # pragma: no cover
+            if app not in self._apps:
+                raise RuntimeError(
+                    "Expected one of the following apps {!r}, got {!r}"
+                    .format(self._apps, app))
         prev = self._current_app
         self._current_app = app
         try:
diff --git a/tests/test_web_functional.py b/tests/test_web_functional.py
index 4999c043912..9354a06fb75 100644
--- a/tests/test_web_functional.py
+++ b/tests/test_web_functional.py
@@ -14,6 +14,7 @@
 import aiohttp
 from aiohttp import (FormData, HttpVersion10, HttpVersion11, TraceConfig,
                      multipart, web)
+from aiohttp.helpers import DEBUG
 
 
 try:
@@ -66,6 +67,8 @@ async def handler(request):
     assert 'OK' == txt
 
 
+@pytest.mark.skipif(not DEBUG,
+                    reason="The check is enabled in debug mode only")
 async def test_handler_returns_not_response(aiohttp_server, aiohttp_client):
     logger = mock.Mock()