diff --git a/src/lsp/iolib.lsp b/src/lsp/iolib.lsp
index d3c43f16e..0e9a7bc6f 100644
--- a/src/lsp/iolib.lsp
+++ b/src/lsp/iolib.lsp
@@ -316,7 +316,7 @@ the one used internally by ECL compiled files."
     ((symbolp mapping)
      (let ((var (intern (symbol-name mapping) (find-package "EXT"))))
        (unless (boundp var)
-	 (set var (ext::make-encoding (load-encoding mapping))))
+	 (setf (symbol-value var) (ext::make-encoding (load-encoding mapping))))
        (symbol-value var)))
     ((consp mapping)
      (let ((output (make-hash-table :size 512 :test 'eq)))