diff --git a/requests_toolbelt/_compat.py b/requests_toolbelt/_compat.py
index 7927a38..21230ee 100644
--- a/requests_toolbelt/_compat.py
+++ b/requests_toolbelt/_compat.py
@@ -49,18 +49,6 @@
     except ImportError:
         from urllib3.contrib import appengine as gaecontrib
 
-if requests.__build__ < 0x021200:
-    PyOpenSSLContext = None
-else:
-    try:
-        from requests.packages.urllib3.contrib.pyopenssl \
-                import PyOpenSSLContext
-    except ImportError:
-        try:
-            from urllib3.contrib.pyopenssl import PyOpenSSLContext
-        except ImportError:
-            PyOpenSSLContext = None
-
 PY3 = sys.version_info > (3, 0)
 
 if PY3:
diff --git a/requests_toolbelt/adapters/x509.py b/requests_toolbelt/adapters/x509.py
index 21bfacb..aff3770 100644
--- a/requests_toolbelt/adapters/x509.py
+++ b/requests_toolbelt/adapters/x509.py
@@ -18,7 +18,6 @@
 from requests.adapters import HTTPAdapter
 import requests
 
-from .._compat import PyOpenSSLContext
 from .. import exceptions as exc
 
 """
@@ -32,6 +31,9 @@
     from _ssl import PROTOCOL_SSLv23 as PROTOCOL
 
 
+PyOpenSSLContext = None
+
+
 class X509Adapter(HTTPAdapter):
     r"""Adapter for use with X.509 certificates.
 
@@ -81,6 +83,7 @@ class X509Adapter(HTTPAdapter):
     """
 
     def __init__(self, *args, **kwargs):
+        self._import_pyopensslcontext()
         self._check_version()
         cert_bytes = kwargs.pop('cert_bytes', None)
         pk_bytes = kwargs.pop('pk_bytes', None)
@@ -118,6 +121,21 @@ def proxy_manager_for(self, *args, **kwargs):
             kwargs['ssl_context'] = self.ssl_context
         return super(X509Adapter, self).proxy_manager_for(*args, **kwargs)
 
+    def _import_pyopensslcontext(self):
+        global PyOpenSSLContext
+
+        if requests.__build__ < 0x021200:
+            PyOpenSSLContext = None
+        else:
+            try:
+                from requests.packages.urllib3.contrib.pyopenssl \
+                        import PyOpenSSLContext
+            except ImportError:
+                try:
+                    from urllib3.contrib.pyopenssl import PyOpenSSLContext
+                except ImportError:
+                    PyOpenSSLContext = None
+
     def _check_version(self):
         if PyOpenSSLContext is None:
             raise exc.VersionMismatchError(
diff --git a/tests/test_x509_adapter.py b/tests/test_x509_adapter.py
index 203bf60..84a10e2 100644
--- a/tests/test_x509_adapter.py
+++ b/tests/test_x509_adapter.py
@@ -24,6 +24,9 @@
 
 REQUESTS_SUPPORTS_SSL_CONTEXT = requests.__build__ >= 0x021200
 
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:'urllib3.contrib.pyopenssl' module is deprecated:DeprecationWarning")
+
 
 class TestX509Adapter(unittest.TestCase):
     """Tests a simple requests.get() call using a .p12 cert.
diff --git a/tox.ini b/tox.ini
index bcf4782..253c8ba 100644
--- a/tox.ini
+++ b/tox.ini
@@ -20,7 +20,7 @@ deps =
     betamax>0.5.0
     trustme
 commands =
-    py.test {posargs}
+    pytest -W error::DeprecationWarning {posargs}
 
 [testenv:noopenssl]
 basepython = python3.7
@@ -31,7 +31,7 @@ deps =
     mock;python_version<"3.3"
     betamax>0.5.0
 commands =
-    py.test {posargs}
+    pytest -W error::DeprecationWarning {posargs}
 
 [testenv:py27-flake8]
 basepython = python2.7