diff --git a/CMakeLists.txt b/CMakeLists.txt
index 36e9c1ee520baf6d0a0f892c5aabadddc9ce1166..fd6a239f3a1c0ef3581f151dbaf5e086e73341be 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -10,13 +10,11 @@ PROJECT(athena
   )
 
 set(CMAKE_CXX_STANDARD 17)
-find_package( DD4hep REQUIRED COMPONENTS DDCore DDG4)
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
 
+find_package(DD4hep REQUIRED COMPONENTS DDCore DDG4)
 find_package(Acts REQUIRED COMPONENTS Core PluginIdentification PluginTGeo PluginDD4hep )
-
-find_package(fmt)
-#find_library(FMT_LIBRARY fmt)
-
+find_package(fmt REQUIRED)
 
 #-----------------------------------------------------------------------------------
 set(a_lib_name athena)
diff --git a/src/FileLoader.cpp b/src/FileLoader.cpp
index d0d60872b9b206ab620e3adbaaf79461cdb079c1..25a5c7e5d019a381b5831958b979edf18927e980 100644
--- a/src/FileLoader.cpp
+++ b/src/FileLoader.cpp
@@ -68,9 +68,9 @@ long load_file(
       "_",
       pos + 1);
     if (after == std::string::npos) after = cache.size(); // cache ends on env var
-    auto env_name = cache.substr(pos + 1, after - pos - 1);
-    auto env_value = std::getenv(env_name.c_str());
-    if (env_value == nullptr) env_value = "";
+    const std::string env_name(cache.substr(pos + 1, after - pos - 1));
+    auto env_ptr = std::getenv(env_name.c_str());
+    const std::string env_value(env_ptr != nullptr ? env_ptr : "");
     cache.erase(pos, after - pos);
     cache.insert(pos, env_value);
     printout(INFO, "FileLoader", "$" + env_name + " -> " + env_value);