diff --git a/include/boost/nowide/cstdlib.hpp b/include/boost/nowide/cstdlib.hpp
index a48028a1..cfdac7cf 100644
--- a/include/boost/nowide/cstdlib.hpp
+++ b/include/boost/nowide/cstdlib.hpp
@@ -21,7 +21,12 @@ namespace nowide {
     ///
     /// \brief UTF-8 aware getenv. Returns 0 if the variable is not set.
     ///
-    /// This function is not thread safe or reenterable as defined by the standard library
+    /// The string pointed to shall not be modified by the program.
+    /// This function is thread-safe as long as no other thread modifies the host environment.
+    /// However subsequent calls to this function might overwrite the string pointed to.
+    ///
+    /// Warning: The returned pointer might only be valid for as long as the calling thread is alive.
+    ///          So avoid passing it across thread boundaries.
     ///
     BOOST_NOWIDE_DECL char* getenv(const char* key);
 
diff --git a/src/cstdlib.cpp b/src/cstdlib.cpp
index ab0d4455..76f0319f 100644
--- a/src/cstdlib.cpp
+++ b/src/cstdlib.cpp
@@ -52,7 +52,7 @@ namespace boost {
 namespace nowide {
     char* getenv(const char* key)
     {
-        static stackstring value;
+        thread_local stackstring value;
 
         const wshort_stackstring name(key);