diff --git a/public/wscript b/public/wscript
index 3840b7b0..da8308f9 100644
--- a/public/wscript
+++ b/public/wscript
@@ -132,7 +132,8 @@ def configure(conf):
 		)
 
 		for export in exports_list:
-			conf.export_define(export)
+			if conf.env[export]:
+				conf.export_define(export)
 
 	# kill temporary uselib
 	del conf.env.DEFINES_export