diff --git a/requests_toolbelt/adapters/host_header_ssl.py b/requests_toolbelt/adapters/host_header_ssl.py
index f34ed1aa..23d615a3 100644
--- a/requests_toolbelt/adapters/host_header_ssl.py
+++ b/requests_toolbelt/adapters/host_header_ssl.py
@@ -14,30 +14,29 @@ class HostHeaderSSLAdapter(HTTPAdapter):
     A HTTPS Adapter for Python Requests that sets the hostname for certificate
     verification based on the Host header.
 
-    This allows requesting the IP address directly via HTTPS without getting
+    This allows requesting the IP address or CNAME directly via HTTPS without getting
     a "hostname doesn't match" exception.
 
     Example usage:
 
         >>> s.mount('https://', HostHeaderSSLAdapter())
-        >>> s.get("https://93.184.216.34", headers={"Host": "example.org"})
-
+        >>> s.get("https://93.184.216.34/", headers={"Host": "example.org"})
+        >>> s.get("https://cname.example.org/", headers={"Host": "example.org"})
     """
 
     def send(self, request, **kwargs):
         # HTTP headers are case-insensitive (RFC 7230)
-        host_header = None
-        for header in request.headers:
-            if header.lower() == "host":
-                host_header = request.headers[header]
-                break
+        # request.headers is a CaseInsensitiveDict
+        host_header = request.headers.get('Host',None)
 
         connection_pool_kwargs = self.poolmanager.connection_pool_kw
 
-        if host_header:
+        if request.url[:5] == "https" and host_header:
             connection_pool_kwargs["assert_hostname"] = host_header
-        elif "assert_hostname" in connection_pool_kwargs:
+            connection_pool_kwargs["server_hostname"] = host_header  # SNI
+        else:
             # an assert_hostname from a previous request may have been left
             connection_pool_kwargs.pop("assert_hostname", None)
+            connection_pool_kwargs.pop("server_hostname", None)  # SNI
 
         return super(HostHeaderSSLAdapter, self).send(request, **kwargs)