diff --git a/requests/adapters.py b/requests/adapters.py
index 2475879c..03aa3b03 100644
--- a/requests/adapters.py
+++ b/requests/adapters.py
@@ -202,7 +202,8 @@ class HTTPAdapter(BaseAdapter):
 
         :param conn: The urllib3 connection object associated with the cert.
         :param url: The requested URL.
-        :param verify: Whether we should actually verify the certificate.
+        :param verify: Whether we should actually verify the certificate
+            or it could be a path to a ca bundle
         :param cert: The SSL certificate to verify.
         """
         if url.lower().startswith('https') and verify:
@@ -216,15 +217,16 @@ class HTTPAdapter(BaseAdapter):
             if not cert_loc:
                 cert_loc = DEFAULT_CA_BUNDLE_PATH
 
-            if not cert_loc:
-                raise Exception("Could not find a suitable SSL CA certificate bundle.")
+            if not cert_loc or not os.path.exists(cert_loc):
+                raise IOError("Could not find a suitable SSL CA certificate bundle, "
+                              "invalid path: {0}".format(cert_loc))
 
             conn.cert_reqs = 'CERT_REQUIRED'
 
-            if not os.path.isdir(cert_loc):
-                conn.ca_certs = cert_loc
-            else:
+            if os.path.isdir(cert_loc):
                 conn.ca_cert_dir = cert_loc
+            else:
+                conn.ca_certs = cert_loc
         else:
             conn.cert_reqs = 'CERT_NONE'
             conn.ca_certs = None
@@ -232,10 +234,15 @@ class HTTPAdapter(BaseAdapter):
 
         if cert:
             if not isinstance(cert, basestring):
-                conn.cert_file = cert[0]
-                conn.key_file = cert[1]
+                conn.cert_file, conn.key_file = cert
             else:
                 conn.cert_file = cert
+            if conn.cert_file and not os.path.exists(conn.cert_file):
+                raise IOError("Could not find the SSL certificate file, "
+                              "invalid path: {0}".format(conn.cert_file))
+            if conn.key_file and not os.path.exists(conn.key_file):
+                raise IOError("Could not find the SSL key file, "
+                              "invalid path: {0}".format(conn.key_file))
 
     def build_response(self, req, resp):
         """Builds a :class:`Response <requests.Response>` object from a urllib3
diff --git a/tests/test_requests.py b/tests/test_requests.py
index 829ab3eb..65f85e03 100755
--- a/tests/test_requests.py
+++ b/tests/test_requests.py
@@ -769,6 +769,22 @@ class TestRequests:
     def test_pyopenssl_redirect(self, httpbin_secure, httpbin_ca_bundle):
         requests.get(httpbin_secure('status', '301'), verify=httpbin_ca_bundle)
 
+    def test_invalid_ca_certificate_path(self):
+        INVALID_PATH = '/garbage'
+        with pytest.raises(IOError) as e:
+            requests.get('http://github.com', verify=INVALID_PATH)
+        assert str(e.value) == 'Could not find a suitable SSL CA certificate bundle, invalid path: {0}'.format(INVALID_PATH)
+
+    def test_invalid_ssl_certificate_files(self):
+        INVALID_PATH = '/garbage'
+        with pytest.raises(IOError) as e:
+            requests.get('http://github.com', cert=INVALID_PATH)
+        assert str(e.value) == 'Could not find the SSL certificate file, invalid path: {0}'.format(INVALID_PATH)
+
+        with pytest.raises(IOError) as e:
+            requests.get('http://github.com', cert=('.', INVALID_PATH))
+        assert str(e.value) == 'Could not find the SSL key file, invalid path: {0}'.format(INVALID_PATH)
+
     def test_https_warnings(self, httpbin_secure, httpbin_ca_bundle):
         """warnings are emitted with requests.get"""
         if HAS_MODERN_SSL or HAS_PYOPENSSL: