diff --git a/src/hydra-queue-runner/dispatcher.cc b/src/hydra-queue-runner/dispatcher.cc
index 8c497a66..d2bb3c90 100644
--- a/src/hydra-queue-runner/dispatcher.cc
+++ b/src/hydra-queue-runner/dispatcher.cc
@@ -31,8 +31,10 @@ void State::makeRunnable(Step::ptr step)
 
 void State::dispatcher()
 {
-    while (true) {
+    printMsg(lvlDebug, "Waiting for the machines parsing to have completed at least once");
+    machinesReadyLock.lock();
 
+    while (true) {
         try {
             printMsg(lvlDebug, "dispatcher woken up");
             nrDispatcherWakeups++;
diff --git a/src/hydra-queue-runner/hydra-queue-runner.cc b/src/hydra-queue-runner/hydra-queue-runner.cc
index 62eb572c..3297730c 100644
--- a/src/hydra-queue-runner/hydra-queue-runner.cc
+++ b/src/hydra-queue-runner/hydra-queue-runner.cc
@@ -158,6 +158,7 @@ void State::monitorMachinesFile()
             (settings.thisSystem == "x86_64-linux" ? "x86_64-linux,i686-linux" : settings.thisSystem.get())
             + " - " + std::to_string(settings.maxBuildJobs) + " 1 "
             + concatStringsSep(",", settings.systemFeatures.get()));
+        machinesReadyLock.unlock();
         return;
     }
 
@@ -203,9 +204,15 @@ void State::monitorMachinesFile()
         parseMachines(contents);
     };
 
+    auto firstParse = true;
+
     while (true) {
         try {
             readMachinesFiles();
+            if (firstParse) {
+                machinesReadyLock.unlock();
+                firstParse = false;
+            }
             // FIXME: use inotify.
             sleep(30);
         } catch (std::exception & e) {
@@ -321,7 +328,7 @@ int State::createSubstitutionStep(pqxx::work & txn, time_t startTime, time_t sto
 
     txn.exec_params0
         ("insert into BuildStepOutputs (build, stepnr, name, path) values ($1, $2, $3, $4)",
-         build->id, stepNr, outputName, 
+         build->id, stepNr, outputName,
          localStore->printStorePath(storePath));
 
     return stepNr;
@@ -770,6 +777,7 @@ void State::run(BuildID buildOne)
         dumpStatus(*conn);
     }
 
+    machinesReadyLock.lock();
     std::thread(&State::monitorMachinesFile, this).detach();
 
     std::thread(&State::queueMonitor, this).detach();
diff --git a/src/hydra-queue-runner/state.hh b/src/hydra-queue-runner/state.hh
index 1eed5a84..8f303d28 100644
--- a/src/hydra-queue-runner/state.hh
+++ b/src/hydra-queue-runner/state.hh
@@ -342,6 +342,7 @@ private:
     nix::Pool<Connection> dbPool;
 
     /* The build machines. */
+    std::mutex machinesReadyLock;
     typedef std::map<std::string, Machine::ptr> Machines;
     nix::Sync<Machines> machines; // FIXME: use atomic_shared_ptr