diff --git a/man/zip_source_window.mdoc b/man/zip_source_window.mdoc
index 6684ced..a6c9524 100644
--- a/man/zip_source_window.mdoc
+++ b/man/zip_source_window.mdoc
@@ -45,13 +45,13 @@
 The
 .Fn zip_source_window_create
 function create a zip source from an underlying zip source,
-restricting access to a particular window starting a byte
+restricting access to a particular window starting at byte
 .Ar start
 and having size
 .Ar len .
-A size
+If
 .Ar len
-of \-1 means "until end of file".
+is \-1, the window spans to the end of the underlying source.
 .Sh RETURN VALUES
 Upon successful completion, the created source is returned.
 Otherwise,