diff --git a/doc/lispref/strings.texi b/doc/lispref/strings.texi
index 6f620c9d769..5e41f8d57bf 100644
--- a/doc/lispref/strings.texi
+++ b/doc/lispref/strings.texi
@@ -436,9 +436,10 @@ display purposes; use @code{truncate-string-to-width} or
 
 @defun string-lines string &optional omit-nulls keep-newlines
 Split @var{string} into a list of strings on newline boundaries.  If
-@var{omit-nulls}, remove empty lines from the results.  if
-@var{keep-newlines}, don't remove the trailing newlines from the
-result strings.
+the optional argument @var{omit-nulls} is non-@code{nil}, remove empty
+lines from the results.  If the optional argument @var{keep-newlines}
+is non-@code{nil}, don't remove the trailing newlines from the result
+strings.
 @end defun
 
 @defun string-pad string length &optional padding start