diff --git a/src/DNS_Mgr.cc b/src/DNS_Mgr.cc
index 903485a652..93eba847cc 100644
--- a/src/DNS_Mgr.cc
+++ b/src/DNS_Mgr.cc
@@ -440,9 +440,14 @@ void DNS_Mgr::InitSource()
 		}
 
 	if ( nb_dns )
-		iosource_mgr->RegisterFd(nb_dns_fd(nb_dns), this);
+		{
+		if ( ! iosource_mgr->RegisterFd(nb_dns_fd(nb_dns), this) )
+			reporter->FatalError("Failed to register nb_dns file descriptor with iosource_mgr");
+		}
 	else
+		{
 		reporter->Warning("problem initializing NB-DNS: %s", err);
+		}
 
 	did_init = true;
 	}
@@ -1490,5 +1495,5 @@ void DNS_Mgr::GetStats(Stats* stats)
 void DNS_Mgr::Terminate()
 	{
 	if ( nb_dns )
-		iosource_mgr->UnregisterFd(nb_dns_fd(nb_dns));
+		iosource_mgr->UnregisterFd(nb_dns_fd(nb_dns), this);
 	}
diff --git a/src/broker/Manager.cc b/src/broker/Manager.cc
index a7ad3a1df6..1e54ce33a0 100644
--- a/src/broker/Manager.cc
+++ b/src/broker/Manager.cc
@@ -207,16 +207,18 @@ void Manager::InitPostScript()
 	auto cqs = get_option("Broker::congestion_queue_size")->AsCount();
 	bstate = std::make_shared<BrokerState>(std::move(config), cqs);
 
-	iosource_mgr->RegisterFd(bstate->subscriber.fd(), this);
-	iosource_mgr->RegisterFd(bstate->status_subscriber.fd(), this);
+	if ( ! iosource_mgr->RegisterFd(bstate->subscriber.fd(), this) )
+		reporter->FatalError("Failed to register broker subscriber with iosource_mgr");
+	if ( ! iosource_mgr->RegisterFd(bstate->status_subscriber.fd(), this) )
+		reporter->FatalError("Failed to register broker status subscriber with iosource_mgr");
 	}
 
 void Manager::Terminate()
 	{
 	FlushLogBuffers();
 
-	iosource_mgr->UnregisterFd(bstate->subscriber.fd());
-	iosource_mgr->UnregisterFd(bstate->status_subscriber.fd());
+	iosource_mgr->UnregisterFd(bstate->subscriber.fd(), this);
+	iosource_mgr->UnregisterFd(bstate->status_subscriber.fd(), this);
 
 	vector<string> stores_to_close;
 
@@ -1503,7 +1505,7 @@ bool Manager::CloseStore(const string& name)
 	if ( s == data_stores.end() )
 		return false;
 
-	iosource_mgr->UnregisterFd(s->second->proxy.mailbox().descriptor());
+	iosource_mgr->UnregisterFd(s->second->proxy.mailbox().descriptor(), this);
 
 	for ( auto i = pending_queries.begin(); i != pending_queries.end(); )
 		if ( i->second->Store().name() == name )
diff --git a/src/iosource/Manager.cc b/src/iosource/Manager.cc
index c5791a2272..66b2beac5f 100644
--- a/src/iosource/Manager.cc
+++ b/src/iosource/Manager.cc
@@ -22,12 +22,13 @@ using namespace iosource;
 
 Manager::WakeupHandler::WakeupHandler()
 	{
-	iosource_mgr->RegisterFd(flare.FD(), this);
+	if ( ! iosource_mgr->RegisterFd(flare.FD(), this) )
+		reporter->FatalError("Failed to register WakeupHandler's fd with iosource_mgr");
 	}
 
 Manager::WakeupHandler::~WakeupHandler()
 	{
-	iosource_mgr->UnregisterFd(flare.FD());
+	iosource_mgr->UnregisterFd(flare.FD(), this);
 	}
 
 void Manager::WakeupHandler::Process()
@@ -207,7 +208,7 @@ void Manager::ConvertTimeout(double timeout, struct timespec& spec)
 		}
 	}
 
-void Manager::RegisterFd(int fd, IOSource* src)
+bool Manager::RegisterFd(int fd, IOSource* src)
 	{
 	struct kevent event;
 	EV_SET(&event, fd, EVFILT_READ, EV_ADD, 0, 0, NULL);
@@ -219,14 +220,16 @@ void Manager::RegisterFd(int fd, IOSource* src)
 		fd_map[fd] = src;
 
 		Wakeup("RegisterFd");
+		return true;
 		}
 	else
 		{
-		DBG_LOG(DBG_MAINLOOP, "Failed to register fd %d from %s: %s", fd, src->Tag(), strerror(errno));
+		reporter->Error("Failed to register fd %d from %s: %s", fd, src->Tag(), strerror(errno));
+		return false;
 		}
 	}
 
-void Manager::UnregisterFd(int fd)
+bool Manager::UnregisterFd(int fd, IOSource* src)
 	{
 	if ( fd_map.find(fd) != fd_map.end() )
 		{
@@ -234,11 +237,17 @@ void Manager::UnregisterFd(int fd)
 		EV_SET(&event, fd, EVFILT_READ, EV_DELETE, 0, 0, NULL);
 		int ret = kevent(event_queue, &event, 1, NULL, 0, NULL);
 		if ( ret != -1 )
-			DBG_LOG(DBG_MAINLOOP, "Unregistered fd %d", fd);
+			DBG_LOG(DBG_MAINLOOP, "Unregistered fd %d from %s", fd, src->Tag());
 
 		fd_map.erase(fd);
 
 		Wakeup("UnregisterFd");
+		return true;
+		}
+	else
+		{
+		reporter->Error("Attempted to unregister an unknown file descriptor %d from %s", fd, src->Tag());
+		return false;
 		}
 	}
 
diff --git a/src/iosource/Manager.h b/src/iosource/Manager.h
index ddf89db11a..1cd8eb965d 100644
--- a/src/iosource/Manager.h
+++ b/src/iosource/Manager.h
@@ -113,12 +113,12 @@ public:
 	 * checked for readiness.
 	 * @param src The IOSource that owns the file descriptor.
 	 */
-	void RegisterFd(int fd, IOSource* src);
+	bool RegisterFd(int fd, IOSource* src);
 
 	/**
 	 * Unregisters a file descriptor from the FindReadySources checks.
 	 */
-	void UnregisterFd(int fd);
+	bool UnregisterFd(int fd, IOSource* src);
 
 	/**
 	 * Forces the poll in FindReadySources to wake up immediately. This method
diff --git a/src/supervisor/Supervisor.cc b/src/supervisor/Supervisor.cc
index 4ef342ffb7..124c9b7771 100644
--- a/src/supervisor/Supervisor.cc
+++ b/src/supervisor/Supervisor.cc
@@ -358,8 +358,11 @@ void Supervisor::HandleChildSignal()
 void Supervisor::InitPostScript()
 	{
 	iosource_mgr->Register(this);
-	iosource_mgr->RegisterFd(signal_flare.FD(), this);
-	iosource_mgr->RegisterFd(stem_pipe->InFD(), this);
+
+	if ( ! iosource_mgr->RegisterFd(signal_flare.FD(), this) )
+		reporter->FatalError("Failed registration for signal_flare with iosource_mgr");
+	if ( ! iosource_mgr->RegisterFd(stem_pipe->InFD(), this) )
+		reporter->FatalError("Failed registration for stem_pipe with iosource_mgr");
 	}
 
 double Supervisor::GetNextTimeout()
diff --git a/src/threading/MsgThread.cc b/src/threading/MsgThread.cc
index 41267147d0..a1aac9ea15 100644
--- a/src/threading/MsgThread.cc
+++ b/src/threading/MsgThread.cc
@@ -181,7 +181,8 @@ MsgThread::MsgThread() : BasicThread(), queue_in(this, 0), queue_out(0, this)
 	failed = false;
 	thread_mgr->AddMsgThread(this);
 
-	iosource_mgr->RegisterFd(flare.FD(), this);
+	if ( ! iosource_mgr->RegisterFd(flare.FD(), this) )
+		reporter->FatalError("Failed to register MsgThread fd with iosource_mgr");
 
 	SetClosed(false);
 	}
@@ -190,7 +191,7 @@ MsgThread::~MsgThread()
 	{
 	// Unregister this thread from the iosource manager so it doesn't wake
 	// up the main poll anymore.
-	iosource_mgr->UnregisterFd(flare.FD());
+	iosource_mgr->UnregisterFd(flare.FD(), this);
 	}
 
 // Set by Bro's main signal handler.