diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 6678b71..28be8a6 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -1355,6 +1355,11 @@
     }
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
 
+    if (ssl->conf->f_rng == NULL) {
+        MBEDTLS_SSL_DEBUG_MSG(1, ("no RNG provided"));
+        return MBEDTLS_ERR_SSL_NO_RNG;
+    }
+
     /* Space for further checks */
 
     return 0;