diff --git a/library/ssl_debug_helpers.h b/library/ssl_debug_helpers.h
index 2fc4163..2ffc5f4 100644
--- a/library/ssl_debug_helpers.h
+++ b/library/ssl_debug_helpers.h
@@ -33,6 +33,8 @@
 
 const char *mbedtls_ssl_states_str( mbedtls_ssl_states in );
 
+const char *mbedtls_ssl_protocol_version_str( mbedtls_ssl_protocol_version in );
+
 const char *mbedtls_tls_prf_types_str( mbedtls_tls_prf_types in );
 
 const char *mbedtls_ssl_key_export_type_str( mbedtls_ssl_key_export_type in );