diff --git a/emper/lib/env.hpp b/emper/lib/env.hpp
index 4d97aaecba060ff8227b19d3930a336a50495e02..5ec0819b2e0b94b6f1f87603e2992b06feaa234e 100644
--- a/emper/lib/env.hpp
+++ b/emper/lib/env.hpp
@@ -9,7 +9,7 @@
 
 namespace emper::lib::env {
 
-static auto getBoolFromEnv(const std::string&& key) -> std::optional<bool> {
+static auto getBoolFromEnv(const std::string& key) -> std::optional<bool> {
 	DBG("parse " << key << " environment variable");
 	char* envVar = std::getenv(key.c_str());
 	if (!envVar) {
@@ -29,7 +29,7 @@ static auto getBoolFromEnv(const std::string&& key) -> std::optional<bool> {
 }
 
 template <typename unsigned_type>
-static auto getUnsignedFromEnv(const std::string&& key) -> std::optional<unsigned_type> {
+static auto getUnsignedFromEnv(const std::string& key) -> std::optional<unsigned_type> {
 	DBG("parse " << key << " environment variable");
 	char* envVar = std::getenv(key.c_str());
 	if (!envVar) {