diff --git a/include/osmocom/gsm/gsm0502.h b/include/osmocom/gsm/gsm0502.h
index c9901df..cb993dc 100644
--- a/include/osmocom/gsm/gsm0502.h
+++ b/include/osmocom/gsm/gsm0502.h
@@ -47,3 +47,7 @@
 };
 
 uint32_t gsm0502_fn_remap(uint32_t fn, enum gsm0502_fn_remap_channel channel);
+
+uint16_t gsm0502_hop_seq_gen(const struct gsm_time *t,
+			     uint8_t hsn, uint8_t maio,
+			     size_t n, const uint16_t *ma);