--- src/include/Rinterface.h	(revision 66251)
+++ src/include/Rinterface.h	(working copy)
@@ -84,7 +84,7 @@ 
 void fpu_setup(Rboolean);
 
 /* in unix/system.c */
-int R_running_as_main_program; 
+extern int R_running_as_main_program; 
 
 #ifdef CSTACK_DEFNS
 /* duplicating Defn.h */