diff --git a/src/condensed.py b/src/condensed.py
--- a/src/condensed.py
+++ b/src/condensed.py
@@ -99,7 +99,7 @@ def run():
 
 	joiner=subparsers.add_parser("join")
 	joiner.add_argument("share",nargs="+",help="shares to be joined")
-	joiner.set_defaults(func=lambda args: print(reconstruct(*args.share)))
+	joiner.set_defaults(func=_reconstruct)
 
 	parser.set_defaults(func=lambda: parser.error("missing command"))
 
@@ -107,5 +107,10 @@ def run():
 	args.func(args)
 
 
+def _reconstruct(args):
+	try: print(reconstruct(*args.share))
+	except ValueError as e: print("operation failed: ",e)
+
+
 if __name__=="__main__":
 	run()