diff --git a/init.lua b/init.lua
index e2bafa0..37b9beb 100644
--- a/init.lua
+++ b/init.lua
@@ -626,7 +626,9 @@ minetest.register_lbm({
 		colorclass == "micro" or colorclass == "slope" then
 			class = colorclass
 			local colorshape = string.sub(name, b+1)
-			local c,d = string.find(colorshape, "dark_") or 0,0
+			local c,d = string.find(colorshape, "dark_")
+			if not c then c = 0 end
+			if not d then d = 0 end
 			local colshapetemp = string.sub(colorshape, d+1)
 			c = string.find(colshapetemp, "_") or 0
 			shape = string.sub(colshapetemp, c)