diff --git a/src/main-export-known-hosts.py b/src/main-export-known-hosts.py
index 45d7e99..86d3185 100644
--- a/src/main-export-known-hosts.py
+++ b/src/main-export-known-hosts.py
@@ -1,4 +1,5 @@
 import argparse
+import os
 import sys
 
 import process_known_hosts
@@ -42,8 +43,16 @@ def main():
 		help = 'write the sshwot file to a given file instead of the stdout'
 	)
 
-	# The required argument
+	try:
+		homedir = os.environ['HOME']
+	except KeyError:
+		raise KeyError('$HOME is not set')
+
+	# The input file
+	# Default to ~/.ssh/known_hosts
 	parser.add_argument('infile',
+		nargs = '?',
+		default = homedir + '/.ssh/known_hosts',
 		help = 'a file in .ssh/known_hosts format'
 	)