diff --git a/doc/rst/source/supplements/seis/sac.rst b/doc/rst/source/supplements/seis/sac.rst
index 73524c0662c..087595bafb1 100644
--- a/doc/rst/source/supplements/seis/sac.rst
+++ b/doc/rst/source/supplements/seis/sac.rst
@@ -241,7 +241,7 @@ To plot seismograms (generated by SAC command ``datagen sub tele *.z``) on a geo
 References
 ----------
 
-Refer to `SAC User Manual <http://ds.iris.edu/files/sac-manual/>`_ for more details
+Refer to `SAC User Manual <https://ds.iris.edu/files/sac-manual/index.html>`_ for more details
 on SAC format and SAC header variables.
 
 Authors