diff --git a/pages/linux/ptx.md b/pages/linux/ptx.md
index 37664f10db..da88ba62f4 100644
--- a/pages/linux/ptx.md
+++ b/pages/linux/ptx.md
@@ -1,6 +1,7 @@
 # ptx
 
 > Generate a permuted index of words from one or more text files.
+> More information: <https://www.gnu.org/software/coreutils/manual/html_node/ptx-invocation.html>.
 
 - Generate a permuted index where the first field of each line is an index reference: