diff --git a/etc/defaults.conf b/etc/defaults.conf
index 230935104ff..7cc90e92f60 100644
--- a/etc/defaults.conf
+++ b/etc/defaults.conf
@@ -97,6 +97,11 @@ XBPS_SUCMD="sudo /bin/sh -c"
 #
 #XBPS_DEBUG_PKGS=yes
 
+# [OPTIONAL]
+# Generate repository binary diffs (deltas) via xdelta3.
+#
+#XBPS_REPO_DELTAS=yes
+
 # [OPTIONAL]
 # Enable or disable global package build options, these options apply
 # to all packages that support the matching options.