diff --git a/src/hydra-queue-runner/build-remote.cc b/src/hydra-queue-runner/build-remote.cc
index d21ab9d7..15c234f3 100644
--- a/src/hydra-queue-runner/build-remote.cc
+++ b/src/hydra-queue-runner/build-remote.cc
@@ -136,8 +136,6 @@ void State::buildRemote(ref<Store> destStore,
         Child child;
         openConnection(machine, tmpDir, logFD.get(), child);
 
-        logFD = -1;
-
         FdSource from(child.from.get());
         FdSink to(child.to.get());
 
@@ -223,6 +221,16 @@ void State::buildRemote(ref<Store> destStore,
 
         autoDelete.cancel();
 
+        /* Truncate the log to get rid of messages about substitutions
+           etc. on the remote system. */
+        if (lseek(logFD.get(), SEEK_SET, 0) != 0)
+            throw SysError("seeking to the start of log file ‘%s’", result.logFile);
+
+        if (ftruncate(logFD.get(), 0) == -1)
+            throw SysError("truncating log file ‘%s’", result.logFile);
+
+        logFD = -1;
+
         /* Do the build. */
         printMsg(lvlDebug, format("building ‘%1%’ on ‘%2%’") % step->drvPath % machine->sshName);