diff --git a/C4/ClassSortRoutine/Dewey.pm b/C4/ClassSortRoutine/Dewey.pm
index 173ad37e03..57f6cce3e4 100644
--- a/C4/ClassSortRoutine/Dewey.pm
+++ b/C4/ClassSortRoutine/Dewey.pm
@@ -67,9 +67,13 @@ sub get_class_sort_key {
     $init =~ s/^([\p{IsAlpha}]+)/$1 /;
     my @tokens = split /\.|\s+/, $init;
     my $digit_group_count = 0;
+    my $first_digit_group_idx;
     for (my $i = 0; $i <= $#tokens; $i++) {
         if ($tokens[$i] =~ /^\d+$/) {
             $digit_group_count++;
+            if (1 == $digit_group_count) {
+                $first_digit_group_idx = $i;
+            }
             if (2 == $digit_group_count) {
                 $tokens[$i] = sprintf("%-15.15s", $tokens[$i]);
                 $tokens[$i] =~ tr/ /0/;
@@ -78,7 +82,7 @@ sub get_class_sort_key {
     }
     # Pad the first digit_group if there was only one
     if (1 == $digit_group_count) {
-        $tokens[0] .= '_000000000000000'
+        $tokens[$first_digit_group_idx] .= '_000000000000000'
     }
     my $key = join("_", @tokens);
     $key =~ s/[^\p{IsAlnum}_]//g;