diff --git a/lib/wall.lua b/lib/wall.lua
index 072dc45..6669d98 100644
--- a/lib/wall.lua
+++ b/lib/wall.lua
@@ -85,7 +85,8 @@ function Wall:update_input()
 			local t = socket.select({ self.socket }, nil, 0)[1]
 			if t then
 
-				local bits = self.socket:receive():match "0901(..).."
+				local rec = self.socket:receive()
+				local bits = rec and rec:match "0901(..).."
 				if bits then
 					local bits = ("0x" .. bits) * 1		-- convert from hex