diff --git a/src/libosmo-mgcp-client/mgcp_client_endpoint_fsm.c b/src/libosmo-mgcp-client/mgcp_client_endpoint_fsm.c
index b8f09d540..a01bbdc32 100644
--- a/src/libosmo-mgcp-client/mgcp_client_endpoint_fsm.c
+++ b/src/libosmo-mgcp-client/mgcp_client_endpoint_fsm.c
@@ -227,7 +227,7 @@ static struct value_string osmo_mgcpc_ep_fsm_event_names[33] = {};
 
 static char osmo_mgcpc_ep_fsm_event_name_bufs[32][32] = {};
 
-static void fill_event_names()
+static void fill_event_names(void)
 {
 	int i;
 	for (i = 0; i < (ARRAY_SIZE(osmo_mgcpc_ep_fsm_event_names) - 1); i++) {
@@ -243,7 +243,7 @@ static void fill_event_names()
 	}
 }
 
-static __attribute__((constructor)) void osmo_mgcpc_ep_fsm_init()
+static __attribute__((constructor)) void osmo_mgcpc_ep_fsm_init(void)
 {
 	OSMO_ASSERT(osmo_fsm_register(&osmo_mgcpc_ep_fsm) == 0);
 	fill_event_names();
diff --git a/src/libosmo-mgcp-client/mgcp_client_fsm.c b/src/libosmo-mgcp-client/mgcp_client_fsm.c
index 1a2b6d8e0..660f0adde 100644
--- a/src/libosmo-mgcp-client/mgcp_client_fsm.c
+++ b/src/libosmo-mgcp-client/mgcp_client_fsm.c
@@ -760,7 +760,7 @@ const char *osmo_mgcpc_conn_peer_name(const struct mgcp_conn_peer *info)
 	return buf;
 }
 
-static __attribute__((constructor)) void osmo_mgcp_client_fsm_init()
+static __attribute__((constructor)) void osmo_mgcp_client_fsm_init(void)
 {
 	OSMO_ASSERT(osmo_fsm_register(&fsm_mgcp_client) == 0);
 }
diff --git a/src/osmo-mgw/mgw_main.c b/src/osmo-mgw/mgw_main.c
index 71b1f1e05..7a76210b4 100644
--- a/src/osmo-mgw/mgw_main.c
+++ b/src/osmo-mgw/mgw_main.c
@@ -95,7 +95,7 @@ static char *config_file = "osmo-mgw.cfg";
 /* used by msgb and mgcp */
 void *tall_mgw_ctx = NULL;
 
-static void print_help()
+static void print_help(void)
 {
 	printf("Some useful options:\n");
 	printf(" -h --help is printing this text.\n");
diff --git a/tests/mgcp/mgcp_test.c b/tests/mgcp/mgcp_test.c
index d843d1033..2d8dfec45 100644
--- a/tests/mgcp/mgcp_test.c
+++ b/tests/mgcp/mgcp_test.c
@@ -2078,7 +2078,7 @@ static void test_mgcp_codec_pt_translate(void)
 	OSMO_ASSERT(ok);
 }
 
-void test_conn_id_matching()
+void test_conn_id_matching(void)
 {
 	struct mgcp_endpoint endp = {};
 	struct mgcp_conn *conn;
@@ -2118,7 +2118,7 @@ void test_conn_id_matching()
 	talloc_free(conn);
 }
 
-void test_e1_trunk_nr_from_epname()
+void test_e1_trunk_nr_from_epname(void)
 {
 	unsigned int trunk_nr;
 	int rc;
@@ -2168,7 +2168,7 @@ void test_e1_trunk_nr_from_epname()
 	return;
 }
 
-void test_mgcp_is_rtp_dummy_payload()
+void test_mgcp_is_rtp_dummy_payload(void)
 {
 	/* realistic rtp packet */
 	static const char rtp_payload[] =
diff --git a/tests/mgcp_client/mgcp_client_test.c b/tests/mgcp_client/mgcp_client_test.c
index 9f09a99be..ef05adc73 100644
--- a/tests/mgcp_client/mgcp_client_test.c
+++ b/tests/mgcp_client/mgcp_client_test.c
@@ -315,7 +315,7 @@ void test_mgcp_msg(void)
 	msgb_free(msg);
 }
 
-void test_mgcp_client_cancel()
+void test_mgcp_client_cancel(void)
 {
 	mgcp_trans_id_t trans_id;
 	struct msgb *msg;
@@ -487,7 +487,7 @@ static struct sdp_section_start_test sdp_section_start_tests[] = {
 	},
 };
 
-void test_sdp_section_start()
+void test_sdp_section_start(void)
 {
 	int i;
 	int failures = 0;