diff --git a/files/reprepro/tails-diff-suites b/files/reprepro/tails-diff-suites
index 2d133f54f975102d62b20d8f7af2b713a0882c4a..b21b66386cc7b3c2fa4ba8c76caef4f4150e1cfb 100755
--- a/files/reprepro/tails-diff-suites
+++ b/files/reprepro/tails-diff-suites
@@ -105,7 +105,7 @@ packages_in_iso() {
 sort_packages_list_inplace() {
    local list="$1"
 
-   sort --stable --key=1 --key=2 --output="$list" "$list"
+   sort --stable --key=1,1 --key=2,2 --output="$list" "$list"
 }
 
 ### Sanity checks