diff --git a/.bam/functions.lua b/.bam/functions.lua
index 5a796da..8c0020f 100644
--- a/.bam/functions.lua
+++ b/.bam/functions.lua
@@ -1,4 +1,6 @@
 
+Import(".bam/utils.lua")
+
 local _systems = {
 	"Win32",
 	"Unix"
@@ -11,6 +13,12 @@ function supported_systems()
 end
 
 
+-- Return True if 'value' is a supported system. False otherwise.
+function valid_system(value)
+	return contains(_systems, value)
+end
+
+
 -- Detect what system we currently are on.
 function system()