diff --git a/include/osmocom/sgsn/gprs_sgsn.h b/include/osmocom/sgsn/gprs_sgsn.h
index 034aebc..e34a019 100644
--- a/include/osmocom/sgsn/gprs_sgsn.h
+++ b/include/osmocom/sgsn/gprs_sgsn.h
@@ -460,6 +460,6 @@
 /* Called on subscriber data updates */
 void sgsn_update_subscriber_data(struct sgsn_mm_ctx *mmctx);
 
-void sgsn_rate_ctr_init();
+void sgsn_rate_ctr_init(void);
 
 #endif /* _GPRS_SGSN_H */