--- a/src/lsp/ffi.lsp
+++ b/src/lsp/ffi.lsp
@@ -668,7 +668,9 @@
 (eval-when (:load-toplevel :execute)
   (defmacro c-inline (args arg-types ret-type &body others)
     `(error "The special form c-inline cannot be used in the interpreter: ~A"
-      (list (list ,@args) ',arg-types ',ret-type ,@others))))
+      (list (list ,@args) ',arg-types ',ret-type ,@others)))
+  (defmacro c-progn (&rest body)
+    '(error "The special form c-progn cannot be used in the interpreter.")))
 
 (defmacro definline (fun arg-types type code)
 "Syntax: (definline symbol (&rest arg-types) result-type &body body) " "