diff --git a/ip.py b/ip.py
index 1dc85bb..2659284 100755
--- a/ip.py
+++ b/ip.py
@@ -149,7 +149,7 @@ class Chunk:
     def gapstr(self, drop='?'):
         """Return contents as a GapString"""
 
-        ret = gapstr.GapString(drop)
+        ret = gapstr.GapString(drop=drop)
         while len(ret) < self.length:
             f = self.collection.get(self.seq + len(ret))
             if f: