diff --git a/src/main/java/net/minecraft/client/network/NetHandlerPlayClient.java b/src/main/java/net/minecraft/client/network/NetHandlerPlayClient.java
index 386a09c..b483a3f 100644
--- a/src/main/java/net/minecraft/client/network/NetHandlerPlayClient.java
+++ b/src/main/java/net/minecraft/client/network/NetHandlerPlayClient.java
@@ -742,6 +742,11 @@
 		float f = (float)(p_147281_1_.func_149028_l() * 360) / 256.0F;
 		float f1 = (float)(p_147281_1_.func_149030_m() * 360) / 256.0F;
 		EntityLivingBase entitylivingbase = (EntityLivingBase)EntityList.createEntityByID(p_147281_1_.func_149025_e(), this.gameController.theWorld);
+		if (entitylivingbase == null)
+		{
+			cpw.mods.fml.common.FMLLog.info("Server attempted to spawn an unknown entity using ID: {0} at ({1}, {2}, {3}) Skipping!", p_147281_1_.func_149025_e(), d0, d1, d2);
+			return;
+		}
 		entitylivingbase.serverPosX = p_147281_1_.func_149023_f();
 		entitylivingbase.serverPosY = p_147281_1_.func_149034_g();
 		entitylivingbase.serverPosZ = p_147281_1_.func_149029_h();
diff --git a/src/main/java/net/minecraft/entity/EntityList.java b/src/main/java/net/minecraft/entity/EntityList.java
index 4a9bb3a..aa5180e 100644
--- a/src/main/java/net/minecraft/entity/EntityList.java
+++ b/src/main/java/net/minecraft/entity/EntityList.java
@@ -84,6 +84,7 @@
 
 	public static void addMapping(Class p_75618_0_, String p_75618_1_, int p_75618_2_)
 	{
+		if (p_75618_2_ < 0 || p_75618_2_ > 255) throw new IllegalArgumentException("Attempted to register a entity with invalid ID: " + p_75618_2_ + " Name: " + p_75618_1_ + " Class: " + p_75618_0_);
 		if (stringToClassMapping.containsKey(p_75618_1_))
 		{
 			throw new IllegalArgumentException("ID is already registered: " + p_75618_1_);