diff --git a/src/lib/ares_qcache.c b/src/lib/ares_qcache.c
index 36d7839d..9725212f 100644
--- a/src/lib/ares_qcache.c
+++ b/src/lib/ares_qcache.c
@@ -121,9 +121,11 @@ static char *ares__qcache_calc_key(const ares_dns_record_t *dnsrec)
       name_len--;
     }
 
-    status = ares__buf_append(buf, (const unsigned char *)name, name_len);
-    if (status != ARES_SUCCESS) {
-      goto fail; /* LCOV_EXCL_LINE: OutOfMemory */
+    if (name_len > 0) {
+      status = ares__buf_append(buf, (const unsigned char *)name, name_len);
+      if (status != ARES_SUCCESS) {
+        goto fail; /* LCOV_EXCL_LINE: OutOfMemory */
+      }
     }
   }
 
diff --git a/src/lib/ares_send.c b/src/lib/ares_send.c
index 94415344..64ff7edd 100644
--- a/src/lib/ares_send.c
+++ b/src/lib/ares_send.c
@@ -62,7 +62,11 @@ static ares_status_t ares_apply_dns0x20(ares_channel_t    *channel,
   }
 
   len = ares_strlen(name);
-  if (len == 0 || len >= sizeof(dns0x20name)) {
+  if (len == 0) {
+    return ARES_SUCCESS;
+  }
+
+  if (len >= sizeof(dns0x20name)) {
     status = ARES_EBADNAME;
     goto done;
   }
diff --git a/src/lib/str/ares__buf.c b/src/lib/str/ares__buf.c
index 08b0ed76..30cc1109 100644
--- a/src/lib/str/ares__buf.c
+++ b/src/lib/str/ares__buf.c
@@ -213,10 +213,14 @@ ares_status_t ares__buf_append(ares__buf_t *buf, const unsigned char *data,
 {
   ares_status_t status;
 
-  if (data == NULL || data_len == 0) {
+  if (data == NULL && data_len != 0) {
     return ARES_EFORMERR;
   }
 
+  if (data_len == 0) {
+    return ARES_SUCCESS;
+  }
+
   status = ares__buf_ensure_space(buf, data_len);
   if (status != ARES_SUCCESS) {
     return status;
diff --git a/test/ares-test-internal.cc b/test/ares-test-internal.cc
index ab8dfd63..846839f6 100644
--- a/test/ares-test-internal.cc
+++ b/test/ares-test-internal.cc
@@ -1021,7 +1021,7 @@ TEST_F(LibraryTest, ArrayMisuse) {
 TEST_F(LibraryTest, BufMisuse) {
   EXPECT_EQ(NULL, ares__buf_create_const(NULL, 0));
   ares__buf_reclaim(NULL);
-  EXPECT_NE(ARES_SUCCESS, ares__buf_append(NULL, NULL, 0));
+  EXPECT_NE(ARES_SUCCESS, ares__buf_append(NULL, NULL, 55));
   size_t len = 10;
   EXPECT_EQ(NULL, ares__buf_append_start(NULL, &len));
   EXPECT_EQ(NULL, ares__buf_append_start(NULL, NULL));
diff --git a/test/ares-test-mock.cc b/test/ares-test-mock.cc
index 5760d0b2..af591a87 100644
--- a/test/ares-test-mock.cc
+++ b/test/ares-test-mock.cc
@@ -817,6 +817,28 @@ TEST_P(MockChannelTest, SearchDomains) {
   EXPECT_EQ("{'www.third.gov' aliases=[] addrs=[2.3.4.5]}", ss.str());
 }
 
+// Issue #858
+TEST_P(CacheQueriesTest, BlankName) {
+  DNSPacket rsp;
+  rsp.set_response().set_aa()
+    .add_question(new DNSQuestion(".", T_SOA))
+    .add_answer(new DNSSoaRR(".", 600, "a.root-servers.net", "nstld.verisign-grs.com", 123456, 3600, 3600, 3600, 3600));
+  EXPECT_CALL(server_, OnRequest("", T_SOA))
+    .WillOnce(SetReply(&server_, &rsp));
+
+  QueryResult result;
+  ares_query_dnsrec(channel_, ".", ARES_CLASS_IN, ARES_REC_TYPE_SOA, QueryCallback, &result, NULL);
+  Process();
+  EXPECT_TRUE(result.done_);
+  EXPECT_EQ(0, result.timeouts_);
+
+  QueryResult cacheresult;
+  ares_query_dnsrec(channel_, ".", ARES_CLASS_IN, ARES_REC_TYPE_SOA, QueryCallback, &cacheresult, NULL);
+  Process();
+  EXPECT_TRUE(cacheresult.done_);
+  EXPECT_EQ(0, cacheresult.timeouts_);
+}
+
 TEST_P(CacheQueriesTest, SearchDomainsCache) {
   DNSPacket nofirst;
   nofirst.set_response().set_aa().set_rcode(NXDOMAIN)