diff --git a/Frameworks/io/src/environment.cc b/Frameworks/io/src/environment.cc
index cd755abc..d03a926f 100644
--- a/Frameworks/io/src/environment.cc
+++ b/Frameworks/io/src/environment.cc
@@ -47,7 +47,7 @@ namespace oak
 
 	std::map<std::string, std::string> const& basic_environment ()
 	{
-		static std::map<std::string, std::string> environment = setup_basic_environment();
+		static std::map<std::string, std::string> const environment = setup_basic_environment();
 		return environment;
 	}