diff --git a/environment-modules.spec b/environment-modules.spec
index 6868c76..d9b81bd 100644
--- a/environment-modules.spec
+++ b/environment-modules.spec
@@ -21,6 +21,7 @@ Patch2:         environment-modules-clear.patch
 Patch3:         environment-modules-avail.patch
 # Fix -Werror=format-security
 # https://bugzilla.redhat.com/show_bug.cgi?id=1037053
+# https://sourceforge.net/p/modules/patches/13/
 Patch4:         environment-modules-format.patch
 
 BuildRequires:  tcl-devel, tclx-devel, libX11-devel