diff --git a/pages/common/optipng.md b/pages/common/optipng.md
index f482e5740..bd96b2aea 100644
--- a/pages/common/optipng.md
+++ b/pages/common/optipng.md
@@ -1,6 +1,7 @@
 # optipng
 
 > PNG image file optimization utility.
+> More information: <http://optipng.sourceforge.net>.
 
 - Compress a PNG with default settings: