diff --git a/scrapy/commands/check.py b/scrapy/commands/check.py
index b8a9ef989..b29587fa7 100644
--- a/scrapy/commands/check.py
+++ b/scrapy/commands/check.py
@@ -6,7 +6,7 @@ from unittest import TextTestRunner, TextTestResult as _TextTestResult
 
 from scrapy.commands import ScrapyCommand
 from scrapy.contracts import ContractsManager
-from scrapy.utils.misc import load_object
+from scrapy.utils.misc import load_object, set_environ
 from scrapy.utils.conf import build_component_list
 
 
@@ -68,16 +68,17 @@ class Command(ScrapyCommand):
 
         spider_loader = self.crawler_process.spider_loader
 
-        for spidername in args or spider_loader.list():
-            spidercls = spider_loader.load(spidername)
-            spidercls.start_requests = lambda s: conman.from_spider(s, result)
+        with set_environ(SCRAPY_CHECK=True):
+            for spidername in args or spider_loader.list():
+                spidercls = spider_loader.load(spidername)
+                spidercls.start_requests = lambda s: conman.from_spider(s, result)
 
-            tested_methods = conman.tested_methods_from_spidercls(spidercls)
-            if opts.list:
-                for method in tested_methods:
-                    contract_reqs[spidercls.name].append(method)
-            elif tested_methods:
-                self.crawler_process.crawl(spidercls)
+                tested_methods = conman.tested_methods_from_spidercls(spidercls)
+                if opts.list:
+                    for method in tested_methods:
+                        contract_reqs[spidercls.name].append(method)
+                elif tested_methods:
+                    self.crawler_process.crawl(spidercls)
 
         # start checks
         if opts.list:
diff --git a/scrapy/utils/misc.py b/scrapy/utils/misc.py
index ddaa7f7bf..7a2cd18ea 100644
--- a/scrapy/utils/misc.py
+++ b/scrapy/utils/misc.py
@@ -1,6 +1,8 @@
 """Helper functions which don't fit anywhere else"""
+import os
 import re
 import hashlib
+from contextlib import contextmanager
 from importlib import import_module
 from pkgutil import iter_modules
 
@@ -10,7 +12,6 @@ from w3lib.html import replace_entities
 from scrapy.utils.python import flatten, to_unicode
 from scrapy.item import BaseItem
 
-
 _ITERABLE_SINGLE_VALUES = dict, BaseItem, six.text_type, bytes
 
 
@@ -40,7 +41,7 @@ def load_object(path):
     except ValueError:
         raise ValueError("Error loading object '%s': not a full path" % path)
 
-    module, name = path[:dot], path[dot+1:]
+    module, name = path[:dot], path[dot + 1:]
     mod = import_module(module)
 
     try:
@@ -85,9 +86,9 @@ def extract_regex(regex, text, encoding='utf-8'):
         regex = re.compile(regex, re.UNICODE)
 
     try:
-        strings = [regex.search(text).group('extract')]   # named group
+        strings = [regex.search(text).group('extract')]  # named group
     except Exception:
-        strings = regex.findall(text)    # full regex or numbered groups
+        strings = regex.findall(text)  # full regex or numbered groups
     strings = flatten(strings)
 
     if isinstance(text, six.text_type):
@@ -142,3 +143,21 @@ def create_instance(objcls, settings, crawler, *args, **kwargs):
         return objcls.from_settings(settings, *args, **kwargs)
     else:
         return objcls(*args, **kwargs)
+
+
+@contextmanager
+def set_environ(**kwargs):
+    """Temporarily set environment variables inside the context manager and
+    fully restore previous environment afterwards
+    """
+
+    original_env = {k: os.environ.get(k) for k in kwargs}
+    os.environ.update(kwargs)
+    try:
+        yield
+    finally:
+        for k, v in original_env:
+            if v is None:
+                del os.environ[k]
+            else:
+                os.environ[k] = v