input should be a const pointer...
diff --git a/aos/build/queues/print_field.rb b/aos/build/queues/print_field.rb
index 8e9521e..7a9fbb4 100644
--- a/aos/build/queues/print_field.rb
+++ b/aos/build/queues/print_field.rb
@@ -18,7 +18,7 @@
 
 namespace aos {
 
-bool PrintField(char *output, size_t *output_bytes, void *input,
+bool PrintField(char *output, size_t *output_bytes, const void *input,
                 size_t *input_bytes, uint32_t type) {
   switch (type) {
 #{TypeNames.collect do |name|