diff --git a/ares__sortaddrinfo.c b/ares__sortaddrinfo.c
index c0e2ea15..58f8a078 100644
--- a/ares__sortaddrinfo.c
+++ b/ares__sortaddrinfo.c
@@ -427,7 +427,7 @@ static int find_src_addr(ares_channel channel,
       return 0;
     }
 
-  if (getsockname(sock, src_addr, &len) == -1)
+  if (getsockname(sock, src_addr, &len) != 0)
     {
       ares__close_socket(channel, sock);
       return -1;
diff --git a/test/ares-test.cc b/test/ares-test.cc
index ec4b4605..9cfb64b3 100644
--- a/test/ares-test.cc
+++ b/test/ares-test.cc
@@ -30,7 +30,8 @@ namespace ares {
 namespace test {
 
 bool verbose = false;
-int mock_port = 5300;
+static constexpr int dynamic_port = 0;
+int mock_port = dynamic_port;
 
 const std::vector<int> both_families = {AF_INET, AF_INET6};
 const std::vector<int> ipv4_family = {AF_INET};
@@ -169,8 +170,8 @@ void DefaultChannelModeTest::Process() {
   ProcessWork(channel_, NoExtraFDs, nullptr);
 }
 
-MockServer::MockServer(int family, int port, int tcpport)
-  : udpport_(port), tcpport_(tcpport ? tcpport : udpport_), qid_(-1) {
+MockServer::MockServer(int family, int port)
+  : udpport_(port), tcpport_(port), qid_(-1) {
   // Create a TCP socket to receive data on.
   tcpfd_ = socket(family, SOCK_STREAM, 0);
   EXPECT_NE(-1, tcpfd_);
@@ -197,6 +198,21 @@ MockServer::MockServer(int family, int port, int tcpport)
     addr.sin_port = htons(udpport_);
     int udprc = bind(udpfd_, (struct sockaddr*)&addr, sizeof(addr));
     EXPECT_EQ(0, udprc) << "Failed to bind AF_INET to UDP port " << udpport_;
+    // retrieve system-assigned port
+    if (udpport_ == dynamic_port) {
+      ares_socklen_t len = sizeof(addr);
+      auto result = getsockname(udpfd_, (struct sockaddr*)&addr, &len);
+      EXPECT_EQ(0, result);
+      udpport_ = ntohs(addr.sin_port);
+      EXPECT_NE(dynamic_port, udpport_);
+    }
+    if (tcpport_ == dynamic_port) {
+      ares_socklen_t len = sizeof(addr);
+      auto result = getsockname(tcpfd_, (struct sockaddr*)&addr, &len);
+      EXPECT_EQ(0, result);
+      tcpport_ = ntohs(addr.sin_port);
+      EXPECT_NE(dynamic_port, tcpport_);
+    }
   } else {
     EXPECT_EQ(AF_INET6, family);
     struct sockaddr_in6 addr;
@@ -209,6 +225,21 @@ MockServer::MockServer(int family, int port, int tcpport)
     addr.sin6_port = htons(udpport_);
     int udprc = bind(udpfd_, (struct sockaddr*)&addr, sizeof(addr));
     EXPECT_EQ(0, udprc) << "Failed to bind AF_INET6 to UDP port " << udpport_;
+    // retrieve system-assigned port
+    if (udpport_ == dynamic_port) {
+      ares_socklen_t len = sizeof(addr);
+      auto result = getsockname(udpfd_, (struct sockaddr*)&addr, &len);
+      EXPECT_EQ(0, result);
+      udpport_ = ntohs(addr.sin6_port);
+      EXPECT_NE(dynamic_port, udpport_);
+    }
+    if (tcpport_ == dynamic_port) {
+      ares_socklen_t len = sizeof(addr);
+      auto result = getsockname(tcpfd_, (struct sockaddr*)&addr, &len);
+      EXPECT_EQ(0, result);
+      tcpport_ = ntohs(addr.sin6_port);
+      EXPECT_NE(dynamic_port, tcpport_);
+    }
   }
   if (verbose) std::cerr << "Configured "
                          << (family == AF_INET ? "IPv4" : "IPv6")
@@ -381,7 +412,8 @@ MockChannelOptsTest::NiceMockServers MockChannelOptsTest::BuildServers(int count
   NiceMockServers servers;
   assert(count > 0);
   for (int ii = 0; ii < count; ii++) {
-    std::unique_ptr<NiceMockServer> server(new NiceMockServer(family, base_port + ii));
+    int port = base_port == dynamic_port ? dynamic_port : base_port + ii;
+    std::unique_ptr<NiceMockServer> server(new NiceMockServer(family, port));
     servers.push_back(std::move(server));
   }
   return servers;
@@ -403,9 +435,9 @@ MockChannelOptsTest::MockChannelOptsTest(int count,
   }
 
   // Point the library at the first mock server by default (overridden below).
-  opts.udp_port = mock_port;
+  opts.udp_port = server_.udpport();
   optmask |= ARES_OPT_UDP_PORT;
-  opts.tcp_port = mock_port;
+  opts.tcp_port = server_.tcpport();
   optmask |= ARES_OPT_TCP_PORT;
 
   // If not already overridden, set short-ish timeouts.
diff --git a/test/ares-test.h b/test/ares-test.h
index a3d1d37c..e92bf3b0 100644
--- a/test/ares-test.h
+++ b/test/ares-test.h
@@ -136,7 +136,7 @@ class DefaultChannelModeTest
 // Mock DNS server to allow responses to be scripted by tests.
 class MockServer {
  public:
-  MockServer(int family, int port, int tcpport = 0);
+  MockServer(int family, int port);
   ~MockServer();
 
   // Mock method indicating the processing of a particular <name, RRtype>