diff --git a/include/osmocom/gsm/cbsp.h b/include/osmocom/gsm/cbsp.h
index d47b37b..90516cb 100644
--- a/include/osmocom/gsm/cbsp.h
+++ b/include/osmocom/gsm/cbsp.h
@@ -283,6 +283,8 @@
 	} u;
 };
 
+extern const __thread char *osmo_cbsp_errstr;
+
 struct msgb *osmo_cbsp_msgb_alloc(void *ctx, const char *name);
 struct msgb *osmo_cbsp_encode(void *ctx, const struct osmo_cbsp_decoded *in);
 struct osmo_cbsp_decoded *osmo_cbsp_decode(void *ctx, struct msgb *in);