diff --git a/SConstruct b/SConstruct
index 1f3dfb5bb..a2760c4a4 100644
--- a/SConstruct
+++ b/SConstruct
@@ -436,6 +436,8 @@ all_cpu_list.sort()
 default_cpus.sort()
 
 def ExtraPathValidator(key, val, env):
+    if not val:
+        return
     paths = val.split(':')
     for path in paths:
         path = os.path.expanduser(path)