diff --git a/djangotoolbox/sites/dynamicsite.py b/djangotoolbox/sites/dynamicsite.py
index 214f867..f782bf2 100644
--- a/djangotoolbox/sites/dynamicsite.py
+++ b/djangotoolbox/sites/dynamicsite.py
@@ -14,11 +14,11 @@ class DynamicSiteIDMiddleware(object):
     def process_request(self, request):
         # Ignore port if it's 80 or 443
         if ':' in request.get_host():
-            domain, port = request.get_host().split(':')
+            domain, port = request.get_host().rsplit(':', 1)
             if int(port) not in (80, 443):
                 domain = request.get_host()
         else:
-            domain = request.get_host().split(':')[0]
+            domain = request.get_host().rsplit(':', 1)[0]
 
         # Domains are case insensitive
         domain = domain.lower()