diff --git a/src/hsp_ag.c b/src/hsp_ag.c
index dd9ef40c3..9bcb994d4 100644
--- a/src/hsp_ag.c
+++ b/src/hsp_ag.c
@@ -122,7 +122,7 @@ static hsp_state_t hsp_state = HSP_IDLE;
 
 static hsp_ag_callback_t hsp_ag_callback;
 
-static void hsp_run();
+static void hsp_run(void);
 static void packet_handler (void * connection, uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size);
 static void handle_query_rfcomm_event(sdp_query_event_t * event, void * context);