diff --git a/build.py b/build.py
index a18a917..a0b626b 100755
--- a/build.py
+++ b/build.py
@@ -2,6 +2,7 @@
 
 import datetime
 import os
+import shutil
 import subprocess
 
 import rwx.file
@@ -20,6 +21,8 @@ def main():
     input_directory = os.path.join(root, 'in')
     out = os.path.join(root, 'out')
     web = os.path.join(out, 'web')
+    if os.path.exists(web):
+        shutil.rmtree(web)
     gen = os.path.join(web, time_id)
     css = os.path.join(gen, style)
     js = os.path.join(gen, script)