diff --git a/src/hydra-queue-runner/hydra-queue-runner.cc b/src/hydra-queue-runner/hydra-queue-runner.cc
index 4e0b9c53..94d36e44 100644
--- a/src/hydra-queue-runner/hydra-queue-runner.cc
+++ b/src/hydra-queue-runner/hydra-queue-runner.cc
@@ -210,7 +210,9 @@ public:
 
     void queueMonitor();
 
-    void getQueuedBuilds(std::shared_ptr<StoreAPI> store, unsigned int & lastBuildId);
+    void getQueuedBuilds(Connection & conn, std::shared_ptr<StoreAPI> store, unsigned int & lastBuildId);
+
+    void removeCancelledBuilds(Connection & conn);
 
     Step::ptr createStep(std::shared_ptr<StoreAPI> store, const Path & drvPath,
         std::set<Step::ptr> & newRunnable);
@@ -389,7 +391,7 @@ void State::queueMonitor()
     unsigned int lastBuildId = 0;
 
     while (true) {
-        getQueuedBuilds(store, lastBuildId);
+        getQueuedBuilds(*conn, store, lastBuildId);
 
         /* Sleep until we get notification from the database about an
            event. */
@@ -403,6 +405,7 @@ void State::queueMonitor()
         }
         if (buildsCancelled.get()) {
             printMsg(lvlError, "got notification: builds cancelled");
+            removeCancelledBuilds(*conn);
         }
     }
 
@@ -410,21 +413,17 @@ void State::queueMonitor()
 }
 
 
-void State::getQueuedBuilds(std::shared_ptr<StoreAPI> store, unsigned int & lastBuildId)
+void State::getQueuedBuilds(Connection & conn, std::shared_ptr<StoreAPI> store, unsigned int & lastBuildId)
 {
     printMsg(lvlError, format("checking the queue for builds > %1%...") % lastBuildId);
 
-    auto conn(dbPool.get());
-
     /* Grab the queued builds from the database, but don't process
        them yet (since we don't want a long-running transaction). */
     std::list<Build::ptr> newBuilds; // FIXME: use queue
 
     {
-        pqxx::work txn(*conn);
+        pqxx::work txn(conn);
 
-        // FIXME: query only builds with ID higher than the previous
-        // highest.
         auto res = txn.parameterized("select * from Builds where id > $1 and finished = 0 order by id")(lastBuildId).exec();
 
         for (auto const & row : res) {
@@ -454,7 +453,7 @@ void State::getQueuedBuilds(std::shared_ptr<StoreAPI> store, unsigned int & last
         if (!store->isValidPath(build->drvPath)) {
             /* Derivation has been GC'ed prematurely. */
             printMsg(lvlInfo, format("aborting GC'ed build %1%") % build->id);
-            pqxx::work txn(*conn);
+            pqxx::work txn(conn);
             txn.parameterized
                 ("update Builds set finished = 1, busy = 0, buildStatus = $2, startTime = $3, stopTime = $3, errorMsg = $4 where id = $1")
                 (build->id)
@@ -476,7 +475,7 @@ void State::getQueuedBuilds(std::shared_ptr<StoreAPI> store, unsigned int & last
 
             printMsg(lvlInfo, format("cached build %1%") % build->id);
 
-            pqxx::work txn(*conn);
+            pqxx::work txn(conn);
             time_t now = time(0);
             markSucceededBuild(txn, build, res, true, now, now);
             txn.commit();
@@ -511,6 +510,30 @@ void State::getQueuedBuilds(std::shared_ptr<StoreAPI> store, unsigned int & last
 }
 
 
+void State::removeCancelledBuilds(Connection & conn)
+{
+    /* Get the current set of queued builds. */
+    std::set<BuildID> currentIds;
+    {
+        pqxx::work txn(conn);
+        auto res = txn.exec("select id from Builds where finished = 0");
+        for (auto const & row : res)
+            currentIds.insert(row["id"].as<BuildID>());
+    }
+
+    auto builds_(builds.lock());
+
+    for (auto i = builds_->begin(); i != builds_->end(); ) {
+        if (currentIds.find(i->first) == currentIds.end()) {
+            printMsg(lvlInfo, format("discarding cancelled build %1%") % i->first);
+            i = builds_->erase(i);
+            // FIXME: ideally we would interrupt active build steps here.
+        } else
+            ++i;
+    }
+}
+
+
 Step::ptr State::createStep(std::shared_ptr<StoreAPI> store, const Path & drvPath,
     std::set<Step::ptr> & newRunnable)
 {
diff --git a/src/lib/Hydra/Helper/Nix.pm b/src/lib/Hydra/Helper/Nix.pm
index 9523ddaa..c54c8f10 100644
--- a/src/lib/Hydra/Helper/Nix.pm
+++ b/src/lib/Hydra/Helper/Nix.pm
@@ -433,6 +433,7 @@ sub cancelBuilds($$) {
             , starttime => $time
             , stoptime => $time
             });
+        $db->storage->dbh->do("notify builds_cancelled");
         return $n;
     });
 }