diff --git a/src/lua/core/computer.lua b/src/lua/core/computer.lua
index b1607dc..a6f8e73 100644
--- a/src/lua/core/computer.lua
+++ b/src/lua/core/computer.lua
@@ -98,23 +98,23 @@ local asciitr = {
 }
 
 local escmap = {
-  A = 200, -- up
-  B = 208, -- down
-  C = 205, -- right
-  D = 203, -- left
+  [65] = 200, -- up
+  [66] = 208, -- down
+  [67] = 205, -- right
+  [68] = 203, -- left
 }
 
-local inesc = 0
+local inesc_down = false
 function computer.signalTransformers.key_down(s, a, ascii, key, user)
   if key ~= -1 then
     return s, a, ascii, key, user
   end
   if ascii == 27 then
-    inesc = true
+    inesc_down = true
     return nil
-  elseif inesc then
-    if ascii < 48 and ascii > 57 and ascii ~= 59 and ascii ~= 91 then
-      inesc = false
+  elseif inesc_down then
+    if (ascii < 48 or ascii > 57) and ascii ~= 59 and ascii ~= 91 then
+      inesc_down = false
       key = escmap[ascii] or 0
       ascii = 0
     else
@@ -124,16 +124,17 @@ function computer.signalTransformers.key_down(s, a, ascii, key, user)
   return s, a, math.floor(asciitr[ascii] or ascii), keymap[ascii] or key, user
 end
 
+local inesc_up = false
 function computer.signalTransformers.key_up(s, a, ascii, key, user)
   if key ~= -1 then
     return s, a, ascii, key, user
   end
   if ascii == 27 then
-    inesc = true
+    inesc_up = true
     return nil
-  elseif inesc then
-    if ascii < 48 and ascii > 57 and ascii ~= 59 and ascii ~= 91 then
-      inesc = false
+  elseif inesc_up then
+    if (ascii < 48 or ascii > 57) and ascii ~= 59 and ascii ~= 91 then
+      inesc_up = false
       key = escmap[ascii] or 0
       ascii = 0
     else
@@ -147,7 +148,7 @@ end
 
 function api.pushSignal(s, ...)
   local result = table.pack(computer.signalTransformers[s](s, ...))
-  if result.n == 0 then return end
+  if result.n == 0 or not result[1] then return end
   result.n = nil
   signalQueue[#signalQueue + 1] = result
 end