diff --git a/update.py b/update.py
index cae387c..96be066 100755
--- a/update.py
+++ b/update.py
@@ -5,10 +5,12 @@ from subprocess import call
 from datetime import datetime
 from typing import List
 
+KEEP_DAYS = 3
 
 def main():
     build_images()
     update_containers()
+    prune()
 
 
 def build_images():
@@ -37,6 +39,10 @@ def read_file(path: Path) -> List[str]:
     return elements
 
 
+def prune():
+    hours = int(KEEP_DAYS * 24)
+    call(['docker', 'system', 'prune', '--all', '--force', '--filter', f'until={hours}h'])
+
 if __name__ == "__main__":
     main()