diff --git a/zipline/_protocol.pyx b/zipline/_protocol.pyx
index 93e6786b..bb91e80b 100644
--- a/zipline/_protocol.pyx
+++ b/zipline/_protocol.pyx
@@ -53,6 +53,8 @@ cdef class check_parameters(object):
 
     def __call__(self, func):
         def assert_keywords_and_call(*args, **kwargs):
+            cdef short i
+
             # verify all the keyword arguments
             for field in kwargs:
                 if field not in self.keyword_names:
@@ -60,21 +62,28 @@ cdef class check_parameters(object):
                                     " '%s'" % (func.__name__, field))
 
             # verify type of each arg
-            for i, arg in enumerate(args[1:]):
-                if isinstance(arg, self.types[i]):
+            i = 0
+            while i < (len(args) - 1):
+                arg = args[i + 1]
+                expected_type = self.types[i]
+
+                if isinstance(arg, expected_type):
+                    i += 1
                     continue
-                elif i in (0, 1) and _is_iterable(arg):
-                    if isinstance(arg[0], self.types[i]):
+
+                elif (i == 0 or i == 1) and _is_iterable(arg):
+                    if isinstance(arg[0], expected_type):
+                        i += 1
                         continue
 
-                expected_type = self.types[i].__name__ \
-                    if not _is_iterable(self.types[i]) \
-                    else ', '.join([type.__name__ for type in self.types[i]])
+                expected_type_name = expected_type.__name__ \
+                    if not _is_iterable(expected_type) \
+                    else ', '.join([type_.__name__ for type_ in expected_type])
 
                 raise TypeError("Expected %s argument to be of type %s%s" %
                                 (self.keyword_names[i],
                                  'or iterable of type ' if i in (0, 1) else '',
-                                 expected_type)
+                                 expected_type_name)
                 )
 
             # verify type of each kwarg