diff --git a/openbsc/include/openbsc/osmux.h b/openbsc/include/openbsc/osmux.h
index 8c01fd0..0e727d5 100644
--- a/openbsc/include/openbsc/osmux.h
+++ b/openbsc/include/openbsc/osmux.h
@@ -22,6 +22,7 @@
 
 int osmux_get_cid(void);
 void osmux_put_cid(uint8_t osmux_cid);
+int osmux_used_cid(void);
 
 enum osmux_state {
 	OSMUX_STATE_DISABLED = 0,
diff --git a/openbsc/src/libmgcp/mgcp_osmux.c b/openbsc/src/libmgcp/mgcp_osmux.c
index 90b7368..b0ef69f 100644
--- a/openbsc/src/libmgcp/mgcp_osmux.c
+++ b/openbsc/src/libmgcp/mgcp_osmux.c
@@ -532,6 +532,20 @@
 /* bsc-nat allocates/releases the Osmux circuit ID */
 static uint8_t osmux_cid_bitmap[16];
 
+int osmux_used_cid(void)
+{
+	int i, j, used = 0;
+
+	for (i = 0; i < sizeof(osmux_cid_bitmap) / 8; i++) {
+		for (j = 0; j < 8; j++) {
+			if (osmux_cid_bitmap[i] & (1 << j))
+				used += 1;
+		}
+	}
+
+	return used;
+}
+
 int osmux_get_cid(void)
 {
 	int i, j;
diff --git a/openbsc/tests/mgcp/mgcp_test.c b/openbsc/tests/mgcp/mgcp_test.c
index b2cb938..7b5de31 100644
--- a/openbsc/tests/mgcp/mgcp_test.c
+++ b/openbsc/tests/mgcp/mgcp_test.c
@@ -1175,6 +1175,31 @@
 	talloc_free(cfg);
 }
 
+static void test_osmux_cid(void)
+{
+	int id, i;
+
+	OSMO_ASSERT(osmux_used_cid() == 0);
+	id = osmux_get_cid();
+	OSMO_ASSERT(id == 0);
+	OSMO_ASSERT(osmux_used_cid() == 1);
+	osmux_put_cid(id);
+	OSMO_ASSERT(osmux_used_cid() == 0);
+
+	for (i = 0; i < 16; ++i) {
+		id = osmux_get_cid();
+		OSMO_ASSERT(id == i);
+		OSMO_ASSERT(osmux_used_cid() == i + 1);
+	}
+
+	id = osmux_get_cid();
+	OSMO_ASSERT(id == -1);
+
+	for (i = 0; i < 256; ++i)
+		osmux_put_cid(i);
+	OSMO_ASSERT(osmux_used_cid() == 0);
+}
+
 int main(int argc, char **argv)
 {
 	osmo_init_logging(&log_info);
@@ -1193,6 +1218,7 @@
 	test_multilple_codec();
 	test_no_cycle();
 	test_no_name();
+	test_osmux_cid();
 
 	printf("Done\n");
 	return EXIT_SUCCESS;