diff --git a/s4cmd.py b/s4cmd.py
index e16960c..3218eba 100755
--- a/s4cmd.py
+++ b/s4cmd.py
@@ -1574,7 +1574,7 @@ def validate(self, format, args):
     }
     fmts = format.split('|')
     if len(fmts) != len(args):
-      raise InvalidArgument('Invalid number of parameters')
+      raise InvalidArgument('Invalid number of parameters, expected %d arguments instead found %d' % (len(fmts), len(args)))
 
     for i, fmt in enumerate(fmts):
       valid = False