diff --git a/libs/sofia-sip/libsofia-sip-ua/sresolv/sres_blocking.c b/libs/sofia-sip/libsofia-sip-ua/sresolv/sres_blocking.c
index 58751b1323..2c55f5a6f3 100644
--- a/libs/sofia-sip/libsofia-sip-ua/sresolv/sres_blocking.c
+++ b/libs/sofia-sip/libsofia-sip-ua/sresolv/sres_blocking.c
@@ -113,6 +113,9 @@ int sres_blocking_update(sres_blocking_t *b,
 {
   int i, N = b->n_sockets;
 
+  if (b == NULL)
+    return -1;
+
   if (old_socket == new_socket) {
     if (old_socket == INVALID_SOCKET) {
       free(b);      /* Destroy us */
@@ -233,11 +236,13 @@ sres_blocking_t *sres_set_blocking(sres_resolver_t *res)
   /* Create a synchronous (blocking) interface towards resolver */
   b = calloc(1, sizeof *b);
 
-  for (i = 0; i < SRES_MAX_NAMESERVERS; i++)
-    b->fds[i].fd = INVALID_SOCKET;
+  if (b) {
+    for (i = 0; i < SRES_MAX_NAMESERVERS; i++)
+      b->fds[i].fd = INVALID_SOCKET;
   
-  if (!sres_resolver_set_async(res, sres_blocking_update, b, 0)) {
-    free(b), b = NULL;
+    if (!sres_resolver_set_async(res, sres_blocking_update, b, 0)) {
+      free(b), b = NULL;
+    }
   }
 
   return b;