diff --git a/libtest/port.cc b/libtest/port.cc
index 54dcffe61..517317adc 100644
--- a/libtest/port.cc
+++ b/libtest/port.cc
@@ -232,7 +232,11 @@ in_port_t get_free_port()
   }
 
   all_socket_fd.last_port= ret_port;
-  release_port(ret_port);
+
+  // Deliberately leave the reservation socket bound (not released) so the
+  // port stays unavailable to other processes' get_free_port() calls until
+  // the caller explicitly release_port()s it, e.g. once its server is
+  // confirmed listening. See libtest::Server::start().
 
   return ret_port;
 }
diff --git a/libtest/server.cc b/libtest/server.cc
index f644465bf..ad243238e 100644
--- a/libtest/server.cc
+++ b/libtest/server.cc
@@ -229,7 +229,14 @@ bool Server::start()
                                 hostname(), port(), "Could not build command()");
   }
 
-  libtest::release_port(_port);
+  // Hold the port reservation (acquired via get_free_port()) until start()
+  // returns by any path -- success, ping timeout, or exception -- so no
+  // other concurrently-running test process's get_free_port() can grab
+  // _port while this server is still starting up.
+  struct PortReservation {
+    in_port_t port;
+    ~PortReservation() { libtest::release_port(port); }
+  } port_reservation{_port};
 
   Application::error_t ret;
   if (Application::SUCCESS !=  (ret= _app.run()))