diff --git a/include/osmocom/gsm/gsm0808.h b/include/osmocom/gsm/gsm0808.h
index b4c7803..dcff415 100644
--- a/include/osmocom/gsm/gsm0808.h
+++ b/include/osmocom/gsm/gsm0808.h
@@ -73,7 +73,7 @@
 struct msgb *gsm0808_create_cipher_complete(struct msgb *layer3, uint8_t alg_id);
 struct msgb *gsm0808_create_cipher_reject(enum gsm0808_cause cause);
 struct msgb *gsm0808_create_cipher_reject_ext(enum gsm0808_cause_class class, uint8_t ext);
-struct msgb *gsm0808_create_classmark_request();
+struct msgb *gsm0808_create_classmark_request(void);
 struct msgb *gsm0808_create_classmark_update(const uint8_t *cm2, uint8_t cm2_len,
 					     const uint8_t *cm3, uint8_t cm3_len);
 struct msgb *gsm0808_create_sapi_reject_cause(uint8_t link_id, uint16_t cause);
@@ -269,8 +269,8 @@
 };
 struct msgb *gsm0808_create_handover_command(const struct gsm0808_handover_command *params);
 
-struct msgb *gsm0808_create_handover_detect();
-struct msgb *gsm0808_create_handover_succeeded();
+struct msgb *gsm0808_create_handover_detect(void);
+struct msgb *gsm0808_create_handover_succeeded(void);
 
 struct gsm0808_handover_complete {
 	bool rr_cause_present;