diff --git a/src/select.cpp b/src/select.cpp
index 7345cbb6..59eb83e0 100644
--- a/src/select.cpp
+++ b/src/select.cpp
@@ -65,6 +65,10 @@ zmq::select_t::handle_t zmq::select_t::add_fd (fd_t fd_, i_poll_events *events_)
     fd_entry_t entry = {fd_, events_};
     fds.push_back (entry);
 
+    //  Ensure we do not attempt to select () on more than FD_SETSIZE
+    //  file descriptors.
+    zmq_assert (fds.size () <= FD_SETSIZE);
+
     //  Start polling on errors.
     FD_SET (fd_, &source_set_err);
 
diff --git a/src/zmq.cpp b/src/zmq.cpp
index 342a8a63..8b21d4be 100644
--- a/src/zmq.cpp
+++ b/src/zmq.cpp
@@ -530,6 +530,10 @@ int zmq_poll (zmq_pollitem_t *items_, int nitems_, long timeout_)
     zmq::fd_t maxfd = zmq::retired_fd;
     zmq::fd_t notify_fd = zmq::retired_fd;
 
+    //  Ensure we do not attempt to select () on more than FD_SETSIZE
+    //  file descriptors.
+    zmq_assert (nitems_ <= FD_SETSIZE);
+
     for (int i = 0; i != nitems_; i++) {
 
         //  0MQ sockets.