diff --git a/code/modules/research/rdmachines.dm b/code/modules/research/rdmachines.dm
index d2a99e9d957..e185fdd6f71 100644
--- a/code/modules/research/rdmachines.dm
+++ b/code/modules/research/rdmachines.dm
@@ -133,4 +133,4 @@
 	overlays -= "[initial(name)]_[stack_name]"
 
 /obj/machinery/r_n_d/proc/check_mat(datum/design/being_built, var/M)
-	return 0
+	return 0 // number of copies of design beign_built you can make with material M