diff --git a/compiler.ss b/compiler.ss
index 2fafc97..be7b80f 100755
--- a/compiler.ss
+++ b/compiler.ss
@@ -35,7 +35,9 @@
                           (if (or (not (pair? subform))
                                   (memq (first subform) '(%apply %car %cdr %cons %bind %if)))
                               (list (simplify-set! `(set! ,(second form) ,subform)))
-                              (list subform))))
+                              (if (and (pair? subform) (eq? (first subform) '%tail-call))
+                                  (list subform) ; The %set! wouldn't be executed anyway.
+                                  (error "set! used with non-value form:" subform)))))
                     '()
                     (cddr value-form)))
         `(%set! ,(second form) ,value-form))))