diff --git a/src/mdbx.c b/src/mdbx.c
index c6c8a41b..480b9a38 100644
--- a/src/mdbx.c
+++ b/src/mdbx.c
@@ -1134,7 +1134,7 @@ const char *__cold mdbx_strerror(int errnum) {
   const char *msg = __mdbx_strerr(errnum);
   if (!msg) {
 #ifdef _MSC_VER
-    static __thread char buffer[1024];
+    static char buffer[1024];
     size_t size = FormatMessageA(
         FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL,
         errnum, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), buffer,
@@ -1142,6 +1142,13 @@ const char *__cold mdbx_strerror(int errnum) {
     if (size)
       msg = buffer;
 #else
+    if (errnum < 0) {
+      static char buffer[32];
+      int rc = snprintf(buffer, sizeof(buffer) - 1, "unknown error %d", errnum);
+      assert(rc > 0);
+      (void)rc;
+      return buffer;
+    }
     msg = strerror(errnum);
 #endif
   }