diff --git a/lib/mu-server.cc b/lib/mu-server.cc
index 2844f281..41c7a7c9 100644
--- a/lib/mu-server.cc
+++ b/lib/mu-server.cc
@@ -78,12 +78,15 @@ struct Server::Private {
 	//
 	// output
 	//
-	void output_sexp(Sexp&& sexp) const
+	void output_sexp(Sexp&& sexp, bool flush = false) const
 	{
 		if (output_)
-			output_(std::move(sexp));
+			output_(std::move(sexp), flush);
+	}
+	void output_sexp(Sexp::List&& lst, bool flush = false) const
+	{
+		output_sexp(Sexp::make_list(std::move(lst)), flush);
 	}
-	void   output_sexp(Sexp::List&& lst) const { output_sexp(Sexp::make_list(std::move(lst))); }
 	size_t output_results(const QueryResults& qres, size_t batch_size) const;
 
 	//
diff --git a/lib/mu-server.hh b/lib/mu-server.hh
index d2784748..811ad6d4 100644
--- a/lib/mu-server.hh
+++ b/lib/mu-server.hh
@@ -33,8 +33,8 @@ namespace Mu {
  *
  */
 class Server {
-      public:
-	using Output = std::function<void(Sexp&& sexp)>;
+public:
+	using Output = std::function<void(Sexp&& sexp, bool flush)>;
 
 	/**
 	 * Construct a new server
@@ -59,7 +59,7 @@ class Server {
 	 */
 	bool invoke(const std::string& expr) noexcept;
 
-      private:
+private:
 	struct Private;
 	std::unique_ptr<Private> priv_;
 };
diff --git a/mu/mu-cmd-server.cc b/mu/mu-cmd-server.cc
index bb39dadd..cfa326c8 100644
--- a/mu/mu-cmd-server.cc
+++ b/mu/mu-cmd-server.cc
@@ -82,7 +82,7 @@ cookie(size_t n)
 }
 
 static void
-output_sexp_stdout(Sexp&& sexp)
+output_sexp_stdout(Sexp&& sexp, bool flush = false)
 {
 	const auto str{sexp.to_sexp_string()};
 	cookie(str.size() + 1);
@@ -90,6 +90,9 @@ output_sexp_stdout(Sexp&& sexp)
 		g_critical("failed to write output '%s'", str.c_str());
 		::raise(SIGTERM); /* terminate ourselves */
 	}
+
+	if (flush)
+		::fflush(::stdout);
 }
 
 static void
@@ -100,7 +103,7 @@ report_error(const Mu::Error& err) noexcept
 	e.add_prop(":error", Sexp::make_number(static_cast<size_t>(err.code())));
 	e.add_prop(":message", Sexp::make_string(err.what()));
 
-	output_sexp_stdout(Sexp::make_list(std::move(e)));
+	output_sexp_stdout(Sexp::make_list(std::move(e)), true /*flush*/);
 }
 
 MuError