diff --git a/nselib/shortport.lua b/nselib/shortport.lua
index 7fc28eddd..101363e10 100644
--- a/nselib/shortport.lua
+++ b/nselib/shortport.lua
@@ -6,6 +6,20 @@
 
 module(... or "shortport", package.seeall)
 
+---
+-- See if a table contains a value.
+-- @param t A table repesenting a set.
+-- @param value The value to check for.
+-- @return True if <code>t</code> contains <code>value</code>, false otherwise.
+local function includes(t, value)
+	for _, elem in ipairs(t) do
+		if elem == value then
+			return true
+		end
+	end
+	return false
+end
+
 --- Return a portrule that returns true when given an open port matching a
 -- single port number or a list of port numbers.
 -- @param port A single port number or a list of port numbers.
@@ -32,17 +46,9 @@ portnumber = function(port, _proto, _state)
 	end	
 
 	return function(host, port)
-		for _, state in pairs(state_table) do
-			if(port.protocol == proto and port.state == state) then
-				for _, _port in ipairs(port_table) do
-					if(port.number == _port) then
-						return true
-					end
-				end
-			end
-		end
-
-		return false
+		return includes(state_table, port.state)
+			and includes(port_table, port.number)
+			and port.protocol == proto
 	end
 end
 
@@ -79,17 +85,9 @@ service = function(service, _proto, _state)
 	end	
 
 	return function(host, port)
-		for _, state in pairs(state_table) do
-			if(port.protocol == proto and port.state == state) then
-				for _, service in ipairs(service_table) do
-					if(port.service == service) then
-						return true
-					end
-				end
-			end
-		end
-
-		return false
+		return includes(state_table, port.state)
+			and includes(service_table, port.service)
+			and port.protocol == proto
 	end
 end
 
@@ -119,14 +117,8 @@ port_or_service = function(_port, _service, proto, _state)
 	end	
 
 	return function(host, port)
-		for _, state in pairs(state_table) do
-			local port_checker = portnumber(_port, proto, state)
-			local service_checker = service(_service, proto, state)
-			if (port_checker(host, port) or service_checker(host, port)) then
-				return true
-			end
-		end
-
-		return false
+		local port_checker = portnumber(_port, proto, state_table)
+		local service_checker = service(_service, proto, state_table)
+		return port_checker(host, port) or service_checker(host, port)
 	end
 end