diff --git a/src/hydra-queue-runner/hydra-queue-runner.cc b/src/hydra-queue-runner/hydra-queue-runner.cc
index 9e5553b6..4e0b9c53 100644
--- a/src/hydra-queue-runner/hydra-queue-runner.cc
+++ b/src/hydra-queue-runner/hydra-queue-runner.cc
@@ -156,10 +156,6 @@ private:
 
     Path hydraData, logDir;
 
-    /* CV for waking up the queue. */
-    std::condition_variable queueMonitorWakeup;
-    std::mutex queueMonitorMutex;
-
     /* The queued builds. */
     typedef std::map<BuildID, Build::ptr> Builds;
     Sync<Builds> builds;
@@ -214,7 +210,7 @@ public:
 
     void queueMonitor();
 
-    void getQueuedBuilds(std::shared_ptr<StoreAPI> store);
+    void getQueuedBuilds(std::shared_ptr<StoreAPI> store, unsigned int & lastBuildId);
 
     Step::ptr createStep(std::shared_ptr<StoreAPI> store, const Path & drvPath,
         std::set<Step::ptr> & newRunnable);
@@ -366,14 +362,47 @@ void State::finishBuildStep(pqxx::work & txn, time_t startTime, time_t stopTime,
 
 void State::queueMonitor()
 {
+    auto conn(dbPool.get());
+
+    struct receiver : public pqxx::notification_receiver
+    {
+        bool status = false;
+        receiver(pqxx::connection_base & c, const std::string & channel)
+            : pqxx::notification_receiver(c, channel) { }
+        void operator() (const string & payload, int pid) override
+        {
+            status = true;
+        };
+        bool get() {
+            bool b = status;
+            status = false;
+            return b;
+        }
+    };
+
+    receiver buildsAdded(*conn, "builds_added");
+    receiver buildsRestarted(*conn, "builds_restarted");
+    receiver buildsCancelled(*conn, "builds_cancelled");
+
     auto store = openStore(); // FIXME: pool
 
-    while (true) {
-        getQueuedBuilds(store);
+    unsigned int lastBuildId = 0;
 
-        {
-            std::unique_lock<std::mutex> lock(queueMonitorMutex);
-            queueMonitorWakeup.wait_for(lock, std::chrono::seconds(5));
+    while (true) {
+        getQueuedBuilds(store, lastBuildId);
+
+        /* Sleep until we get notification from the database about an
+           event. */
+        conn->await_notification();
+
+        if (buildsAdded.get())
+            printMsg(lvlError, "got notification: new builds added to the queue");
+        if (buildsRestarted.get()) {
+            printMsg(lvlError, "got notification: builds restarted");
+            lastBuildId = 0; // check all builds
+        }
+        if (buildsCancelled.get()) {
+            printMsg(lvlError, "got notification: builds cancelled");
         }
     }
 
@@ -381,9 +410,9 @@ void State::queueMonitor()
 }
 
 
-void State::getQueuedBuilds(std::shared_ptr<StoreAPI> store)
+void State::getQueuedBuilds(std::shared_ptr<StoreAPI> store, unsigned int & lastBuildId)
 {
-    printMsg(lvlError, "checking the queue...");
+    printMsg(lvlError, format("checking the queue for builds > %1%...") % lastBuildId);
 
     auto conn(dbPool.get());
 
@@ -396,11 +425,12 @@ void State::getQueuedBuilds(std::shared_ptr<StoreAPI> store)
 
         // FIXME: query only builds with ID higher than the previous
         // highest.
-        auto res = txn.exec("select * from Builds where finished = 0 order by id");
+        auto res = txn.parameterized("select * from Builds where id > $1 and finished = 0 order by id")(lastBuildId).exec();
 
         for (auto const & row : res) {
             auto builds_(builds.lock());
             BuildID id = row["id"].as<BuildID>();
+            if (id > lastBuildId) lastBuildId = id;
             if (has(*builds_, id)) continue;
 
             auto build = std::make_shared<Build>();
diff --git a/src/hydra-queue-runner/pool.hh b/src/hydra-queue-runner/pool.hh
index 0a58ebe0..a1cd3977 100644
--- a/src/hydra-queue-runner/pool.hh
+++ b/src/hydra-queue-runner/pool.hh
@@ -57,7 +57,7 @@ public:
             if (r) state_->idle.push_back(r);
         }
 
-        R * operator -> () { return r; }
+        R * operator -> () { return r.get(); }
         R & operator * () { return *r; }
     };
 
diff --git a/src/lib/Hydra/Helper/Nix.pm b/src/lib/Hydra/Helper/Nix.pm
index 7a68490f..9523ddaa 100644
--- a/src/lib/Hydra/Helper/Nix.pm
+++ b/src/lib/Hydra/Helper/Nix.pm
@@ -469,6 +469,8 @@ sub restartBuilds($$) {
         # FIXME: Add this to the API.
         # FIXME: clear the dependencies?
         $db->resultset('FailedPaths')->search({ path => [ @paths ]})->delete;
+
+        $db->storage->dbh->do("notify builds_restarted");
     });
 
     return scalar(@buildIds);
diff --git a/src/script/hydra-evaluator b/src/script/hydra-evaluator
index 9d463122..bcdb948e 100755
--- a/src/script/hydra-evaluator
+++ b/src/script/hydra-evaluator
@@ -246,6 +246,8 @@ sub checkJobsetWrapped {
         $jobset->update({ enabled => 0 }) if $jobset->enabled == 2;
 
         $jobset->update({ lastcheckedtime => time });
+
+        $db->storage->dbh->do("notify builds_added");
     });
 
     # Store the error messages for jobs that failed to evaluate.