diff --git a/libsrc/common/ftell.c b/libsrc/common/ftell.c
index 4e4746e03..9882cfc05 100644
--- a/libsrc/common/ftell.c
+++ b/libsrc/common/ftell.c
@@ -26,7 +26,7 @@ long __fastcall__ ftell (register FILE* f)
 
     /* Is the file open? */
     if ((f->f_flags & _FOPEN) == 0) {
-        _errno = EINVAL;                /* File not open */
+        _seterrno (EINVAL);                /* File not open */
         return -1L;
     }