--- /dev/null
+--- a/gettext-tools/libgettextpo/error.h
++++ b/gettext-tools/libgettextpo/error.h
+@@ -58,7 +58,7 @@ extern void error_at_line (int __status,
+ /* If NULL, error will flush stdout, then print on stderr the program
+ name, a colon and a space. Otherwise, error will call this
+ function without parameters instead. */
+-void (*error_print_progname) (void);
++extern void (*error_print_progname) (void);
+
+ /* This variable is incremented each time 'error' is called. */
+ extern DLL_VARIABLE unsigned int error_message_count;