diff --git a/pyren/doc_maker.py b/pyren/doc_maker.py
index a3e2432..70f9030 100755
--- a/pyren/doc_maker.py
+++ b/pyren/doc_maker.py
@@ -677,7 +677,8 @@ def optParser():
   parser.add_argument("--sd",
       help="separate doc files",
       dest="sd",
-      default=False)
+      default=False,
+      action="store_true")
 
   parser.add_argument("--cfc",
       help="turn off automatic FC and do it by script",
diff --git a/pyren/pyren.py b/pyren/pyren.py
index 9e2e90a..278dc78 100755
--- a/pyren/pyren.py
+++ b/pyren/pyren.py
@@ -95,7 +95,8 @@ def optParser():
   parser.add_argument("--sd",
       help="separate doc files",
       dest="sd",
-      default=False)
+      default=False,
+      action="store_true")
 
   parser.add_argument("-m",
       help="number of car model",