diff --git a/lib/core-net/output.c b/lib/core-net/output.c
index b329f8018..845628133 100644
--- a/lib/core-net/output.c
+++ b/lib/core-net/output.c
@@ -196,7 +196,9 @@ int lws_issue_raw(struct lws *wsi, unsigned char *buf, size_t len)
 	lwsl_debug("%p new partial sent %d from %lu total\n", wsi, m,
 		    (unsigned long)real_len);
 
-	lws_buflist_append_segment(&wsi->buflist_out, buf + m, real_len - m);
+	if (lws_buflist_append_segment(&wsi->buflist_out, buf + m,
+				       real_len - m) < 0)
+		return -1;
 
 	lws_stats_atomic_bump(wsi->context, pt, LWSSTATS_C_WRITE_PARTIALS, 1);
 	lws_stats_atomic_bump(wsi->context, pt,
diff --git a/lib/tls/mbedtls/lws-genrsa.c b/lib/tls/mbedtls/lws-genrsa.c
index 5eb6c5b75..73c40cd75 100644
--- a/lib/tls/mbedtls/lws-genrsa.c
+++ b/lib/tls/mbedtls/lws-genrsa.c
@@ -146,8 +146,9 @@ lws_genrsa_new_keypair(struct lws_context *context, struct lws_genrsa_ctx *ctx,
 				if (!el[n].buf)
 					goto cleanup;
 				el[n].len = mbedtls_mpi_size(mpi[n]);
-				mbedtls_mpi_write_binary(mpi[n], el[n].buf,
-							 el[n].len);
+				if (mbedtls_mpi_write_binary(mpi[n], el[n].buf,
+							 el[n].len))
+					goto cleanup;
 			}
 	}