diff --git a/SoObjects/Mailer/SOGoMailObject.h b/SoObjects/Mailer/SOGoMailObject.h
index 2d412e47c..5b53c4f54 100644
--- a/SoObjects/Mailer/SOGoMailObject.h
+++ b/SoObjects/Mailer/SOGoMailObject.h
@@ -51,7 +51,7 @@
 
 @class WOResponse;
 
-NSArray *SOGoMailCoreInfoKeys;
+extern NSArray *SOGoMailCoreInfoKeys;
 
 @interface SOGoMailObject : SOGoMailBaseObject
 {