diff --git a/example/calculator.cpp b/example/calculator.cpp
index 956a5d60..65f6476e 100644
--- a/example/calculator.cpp
+++ b/example/calculator.cpp
@@ -30,9 +30,9 @@ class InitImpl : public Init
     }
 };
 
-void LogPrint(bool raise, std::string message)
+void LogPrint(bool raise, const std::string& message)
 {
-    if (raise) throw std::runtime_error(std::move(message));
+    if (raise) throw std::runtime_error(message);
     std::ofstream("debug.log", std::ios_base::app) << message << std::endl;
 }
 
diff --git a/example/example.cpp b/example/example.cpp
index 3c8a7479..ecaabafb 100644
--- a/example/example.cpp
+++ b/example/example.cpp
@@ -23,9 +23,9 @@ auto Spawn(mp::EventLoop& loop, const std::string& process_argv0, const std::str
     return std::make_tuple(mp::ConnectStream<InitInterface>(loop, fd), pid);
 }
 
-void LogPrint(bool raise, std::string message)
+void LogPrint(bool raise, const std::string& message)
 {
-    if (raise) throw std::runtime_error(std::move(message));
+    if (raise) throw std::runtime_error(message);
     std::ofstream("debug.log", std::ios_base::app) << message << std::endl;
 }
 
diff --git a/example/printer.cpp b/example/printer.cpp
index f24f60c2..0a51cdd4 100644
--- a/example/printer.cpp
+++ b/example/printer.cpp
@@ -24,9 +24,9 @@ class InitImpl : public Init
     std::unique_ptr<Printer> makePrinter() override { return std::make_unique<PrinterImpl>(); }
 };
 
-void LogPrint(bool raise, std::string message)
+void LogPrint(bool raise, const std::string& message)
 {
-    if (raise) throw std::runtime_error(std::move(message));
+    if (raise) throw std::runtime_error(message);
     std::ofstream("debug.log", std::ios_base::app) << message << std::endl;
 }
 
diff --git a/include/mp/proxy-types.h b/include/mp/proxy-types.h
index 4679f8d2..902bd240 100644
--- a/include/mp/proxy-types.h
+++ b/include/mp/proxy-types.h
@@ -159,7 +159,7 @@ auto PassField(Priority<1>, TypeList<>, ServerContext& server_context, const Fn&
 
     auto thread_client = context_arg.getThread();
     return JoinPromises(server.m_context.connection->m_threads.getLocalServer(thread_client)
-                            .then([&server, invoke, req](kj::Maybe<Thread::Server&> perhaps) {
+                            .then([&server, invoke, req](const kj::Maybe<Thread::Server&>& perhaps) {
                                 KJ_IF_MAYBE(thread_server, perhaps)
                                 {
                                     const auto& thread = static_cast<ProxyServer<Thread>&>(*thread_server);