diff --git a/inc/wspr.h b/inc/wspr.h
--- a/inc/wspr.h
+++ b/inc/wspr.h
@@ -5,7 +5,7 @@
 void wspr_init(void);
 void wspr_sleep(void);
 void wspr_wakeup(void);
-void wspr_transmit(uint8_t* grid_locator);
+void wspr_transmit(uint8_t* grid_locator, uint8_t send_alternate);
 
 
 #endif