diff --git a/mods/ENTITIES/mcl_mobs/api.txt b/mods/ENTITIES/mcl_mobs/api.txt
index 3d3ac8632..29cdc2c48 100644
--- a/mods/ENTITIES/mcl_mobs/api.txt
+++ b/mods/ENTITIES/mcl_mobs/api.txt
@@ -671,6 +671,13 @@ mob will spawn e.g.
 mobs_animal:sheep_chance 11000
 mobs_monster:sand_monster_chance 100
 
+Registering Mob Conversion
+----------------
+
+Sometimes you need to completely replace one mob with a different version. To do this, use:
+
+	mcl_mobs.register_conversion(old_name, new_name)
+
 
 Rideable Horse Example Mob
 --------------------------
diff --git a/mods/ENTITIES/mcl_mobs/init.lua b/mods/ENTITIES/mcl_mobs/init.lua
index 3a2e18872..44eae7b13 100644
--- a/mods/ENTITIES/mcl_mobs/init.lua
+++ b/mods/ENTITIES/mcl_mobs/init.lua
@@ -342,6 +342,17 @@ function mcl_mobs.register_mob(name, def)
 	minetest.register_entity(name, setmetatable(final_def,mcl_mobs.mob_class_meta))
 end -- END mcl_mobs.register_mob function
 
+function mcl_mobs.register_conversion(old_name, new_name)
+	minetest.register_entity(old_name, {
+		on_activate = function(self, staticdata, dtime)
+			local obj = minetest.add_entity(self.object:get_pos(), new_name, staticdata)
+			local hook = (obj:get_luaentity() or {})._on_after_convert
+			if hook then hook(obj) end
+			self.object:remove()
+		end,
+		_convert_to = new_name,
+	})
+end
 
 function mcl_mobs.get_arrow_damage_func(damage, typ)
 	local typ = mcl_damage.types[typ] and typ or "arrow"
diff --git a/mods/ENTITIES/mobs_mc/rover.lua b/mods/ENTITIES/mobs_mc/rover.lua
index 68d13669d..d1f21ffd0 100644
--- a/mods/ENTITIES/mobs_mc/rover.lua
+++ b/mods/ENTITIES/mobs_mc/rover.lua
@@ -491,20 +491,17 @@ mcl_mobs.register_mob("mobs_mc:rover", {
 	view_range = 64,
 	fear_height = 4,
 	attack_type = "dogfight",
-})
-
--- compat
-minetest.register_entity("mobs_mc:enderman", {
-	on_activate = function(self, staticdata, dtime)
-		local obj = minetest.add_entity(self.object:get_pos(), "mobs_mc:rover", staticdata)
+	_on_after_convert = function(obj)
 		obj:set_properties({
 			mesh = "vl_rover.b3d",
 			textures = { "vl_mobs_rover.png^vl_mobs_rover_face.png" },
 			visual_size = {x=10, y=10},
 		})
-		self.object:remove()
-	end,
-})
+	end
+}) -- END mcl_mobs.register_mob("mobs_mc:rover", {
+
+-- compat
+mcl_mobs.register_conversion("mobs_mc:enderman", "mobs_mc:rover")
 
 -- End spawn
 mcl_mobs:spawn_specific(
diff --git a/mods/ENTITIES/mobs_mc/stalker.lua b/mods/ENTITIES/mobs_mc/stalker.lua
index 69fad180a..5b1fd6a08 100644
--- a/mods/ENTITIES/mobs_mc/stalker.lua
+++ b/mods/ENTITIES/mobs_mc/stalker.lua
@@ -175,7 +175,18 @@ mcl_mobs.register_mob("mobs_mc:stalker", {
 	floats = 1,
 	fear_height = 4,
 	view_range = 16,
-})
+
+	_on_after_convert = function(obj)
+		obj:set_properties({
+			visual_size = {x=2, y=2},
+			mesh = "vl_stalker.b3d",
+			textures = {
+				{get_texture({}),
+				"mobs_mc_empty.png"},
+			},
+		})
+	end,
+}) -- END mcl_mobs.register_mob("mobs_mc:stalker", {
 
 mcl_mobs.register_mob("mobs_mc:stalker_overloaded", {
 	description = S("Overloaded Stalker"),
@@ -304,26 +315,8 @@ mcl_mobs.register_mob("mobs_mc:stalker_overloaded", {
 	--Having trouble when fire is placed with lightning
 	fire_resistant = true,
 	glow = 3,
-})
 
--- compat
-minetest.register_entity("mobs_mc:creeper", {
-	on_activate = function(self, staticdata, dtime)
-		local obj = minetest.add_entity(self.object:get_pos(), "mobs_mc:stalker", staticdata)
-		obj:set_properties({
-			visual_size = {x=2, y=2},
-			mesh = "vl_stalker.b3d",
-			textures = {
-				{get_texture({}),
-				"mobs_mc_empty.png"},
-			},
-		})
-		self.object:remove()
-	end,
-})
-minetest.register_entity("mobs_mc:creeper_charged", {
-	on_activate = function(self, staticdata, dtime)
-		local obj = minetest.add_entity(self.object:get_pos(), "mobs_mc:stalker_overloaded", staticdata)
+	_on_after_convert = function(obj)
 		obj:set_properties({
 			visual_size = {x=2, y=2},
 			mesh = "vl_stalker.b3d",
@@ -332,9 +325,12 @@ minetest.register_entity("mobs_mc:creeper_charged", {
 				AURA},
 			},
 		})
-		self.object:remove()
 	end,
-})
+}) -- END mcl_mobs.register_mob("mobs_mc:stalker_overloaded", {
+
+-- compat
+mcl_mobs.register_conversion("mobs_mc:creeper", "mobs_mc:stalker")
+mcl_mobs.register_conversion("mobs_mc:creeper_charged", "mobs_mc:stalker_overloaded")
 
 mcl_mobs:spawn_specific(
 "mobs_mc:stalker",
diff --git a/mods/ITEMS/mcl_mobspawners/init.lua b/mods/ITEMS/mcl_mobspawners/init.lua
index ae6326009..f32558629 100644
--- a/mods/ITEMS/mcl_mobspawners/init.lua
+++ b/mods/ITEMS/mcl_mobspawners/init.lua
@@ -63,8 +63,8 @@ local function set_doll_properties(doll, mob)
 		xs = doll_size_overrides[mob].x
 		ys = doll_size_overrides[mob].y
 	else
-		xs = mobinfo.visual_size.x * 0.33333
-		ys = mobinfo.visual_size.y * 0.33333
+		xs = (mobinfo.visual_size.x or 0) * 0.33333
+		ys = (mobinfo.visual_size.y or 0) * 0.33333
 	end
 	local prop = {
 		mesh = mobinfo.mesh,
@@ -358,6 +358,11 @@ doll_def.on_activate = function(self, staticdata, dtime_s)
 	if mob == "" or mob == nil then
 		mob = default_mob
 	end
+
+	-- Handle conversion of mob spawners
+	local convert_to = (minetest.registered_entities[mob] or {})._convert_to
+	if convert_to then mob = convert_to end
+
 	set_doll_properties(self.object, mob)
 	self.object:set_velocity({x=0, y=0, z=0})
 	self.object:set_acceleration({x=0, y=0, z=0})
@@ -390,3 +395,11 @@ minetest.register_lbm({
 		respawn_doll(pos)
 	end,
 })
+
+minetest.register_on_mods_loaded(function()
+	for name,mobinfo in pairs(minetest.registered_entities) do
+		if ( mobinfo.is_mob or name:find("mobs_mc") ) and not ( mobinfo.visual_size or mobinfo._convert_to ) then
+			minetest.log("warning", "Definition for "..tostring(name).." is missing field 'visual_size', mob spawners will not work properly")
+		end
+	end
+end)