diff --git a/sim/network.lua b/sim/network.lua
index d1759b5..3645a4b 100644
--- a/sim/network.lua
+++ b/sim/network.lua
@@ -75,7 +75,7 @@ function network_update()
 				local logic = data[i+5]
 				local input = data[i+6]
 				local global = data[i+7]
-				local numports = tonumber(data[i+8])
+				local numports = tonumber(data[i+8]) or error("no portcount for gate "..(data[i+2])
 				i = i + 8
 				
 				local ports = {}