diff --git a/TOOLS/matroska.pl b/TOOLS/matroska.pl
index 28ad1197c5..41e4f6aa81 100755
--- a/TOOLS/matroska.pl
+++ b/TOOLS/matroska.pl
@@ -64,7 +64,7 @@ sub generate_c_header {
 
         # Output a counter variable for each element
         # (presence/absence for scalars, item count for arrays)
-        for my $subel (values %{$el->{subelements}}) {
+        for my $subel (sort values %{$el->{subelements}}) {
             print "    int n_$subel->{fieldname};\n"
         }
         print "};\n";