diff --git a/compiler/pgates/pdriver.py b/compiler/pgates/pdriver.py
index 5b4a6c9a..02e4355c 100644
--- a/compiler/pgates/pdriver.py
+++ b/compiler/pgates/pdriver.py
@@ -11,7 +11,7 @@ class pdriver(pgate.pgate):
     """
     This instantiates an even or odd number of inverters sized for driving a load.
     """
-    def __init__(self, name, neg_polarity=False, fanout=1, size_list=None, height=None):
+    def __init__(self, name, neg_polarity=False, fanout=0, size_list=None, height=None):
 
         self.stage_effort = 3
         self.height = height 
@@ -19,6 +19,8 @@ class pdriver(pgate.pgate):
         self.size_list = size_list
         self.fanout = fanout
 
+        if size_list == None and self.fanout == 0:
+            debug.error("Either fanout or size list must be specified.", -1)
         if self.size_list and self.fanout != 0:
             debug.error("Cannot specify both size_list and fanout.", -1)
         if self.size_list and self.neg_polarity: