diff --git a/python/flatbuffers/builder.py b/python/flatbuffers/builder.py
index f9448b0bc..c5978bddb 100644
--- a/python/flatbuffers/builder.py
+++ b/python/flatbuffers/builder.py
@@ -113,7 +113,7 @@ class Builder(object):
     MAX_BUFFER_SIZE = 2**31
     ## @endcond
 
-    def __init__(self, initialSize):
+    def __init__(self, initialSize=1024):
         """Initializes a Builder of size `initial_size`.
 
         The internal buffer is grown as needed.