diff --git a/mods/ITEMS/mcl_stairs/api.lua b/mods/ITEMS/mcl_stairs/api.lua
index c580e2bba..390461c6c 100644
--- a/mods/ITEMS/mcl_stairs/api.lua
+++ b/mods/ITEMS/mcl_stairs/api.lua
@@ -262,8 +262,8 @@ function mcl_stairs.register_slab(subname, recipeitem, groups, images, descripti
 			-- combine two slabs if possible
 			-- Requirements: Same slab material, must be placed on top of lower slab, or on bottom of upper slab
 			if (wield_item == unode.name or (udefs and wield_item == udefs._mcl_other_slab_half)) and
-					not ((dir.y >= 0 and minetest.get_item_group(under.name, "slab_top") == 1) or
-					(dir.y <= 0 and minetest.get_item_group(under.name, "slab_top") == 0)) then
+					not ((dir.y >= 0 and minetest.get_item_group(unode.name, "slab_top") == 1) or
+					(dir.y <= 0 and minetest.get_item_group(unode.name, "slab_top") == 0)) then
 
 				minetest.set_node(under, {name = double_slab, param2 = p2})
 
@@ -271,7 +271,7 @@ function mcl_stairs.register_slab(subname, recipeitem, groups, images, descripti
 					itemstack:take_item()
 				end
 				return itemstack
-			elseif (wield_item == anode.name or (adefs and adefs._mcl_other_slab_half)) then
+			elseif (wield_item == anode.name or (adefs and wield_item == adefs._mcl_other_slab_half)) then
 				minetest.set_node(above, {name = double_slab, param2 = p2})
 
 				if not creative_enabled then