diff --git a/zipline/transforms/mavg.py b/zipline/transforms/mavg.py
index 06233992..2a35e968 100644
--- a/zipline/transforms/mavg.py
+++ b/zipline/transforms/mavg.py
@@ -29,10 +29,12 @@ class MovingAverage(object):
     """
     __metaclass__ = TransformMeta
 
-    def __init__(self, fields,
+    def __init__(self, fields='price',
                  market_aware=True, window_length=None, delta=None):
-
+        if isinstance(fields, basestring):
+            fields = [fields]
         self.fields = fields
+
         self.market_aware = market_aware
 
         self.delta = delta
diff --git a/zipline/transforms/stddev.py b/zipline/transforms/stddev.py
index 992ed481..2b928c19 100644
--- a/zipline/transforms/stddev.py
+++ b/zipline/transforms/stddev.py
@@ -31,11 +31,13 @@ class MovingStandardDev(object):
     """
     __metaclass__ = TransformMeta
 
-    def __init__(self, fields,
+    def __init__(self, fields='price',
                  market_aware=True, window_length=None, delta=None):
+        if isinstance(fields, basestring):
+            fields = [fields]
+        self.fields = fields
 
         self.market_aware = market_aware
-        self.fields = fields
 
         self.delta = delta
         self.window_length = window_length