diff --git a/include/picrin/proc.h b/include/picrin/proc.h
index 7d6dcd92..c29b6c36 100644
--- a/include/picrin/proc.h
+++ b/include/picrin/proc.h
@@ -19,6 +19,8 @@ struct pic_proc {
   pic_value aux;
 };
 
+#define pic_proc_p(o) (pic_type(o) == PIC_TT_PROC)
+
 #define pic_proc_ptr(o) ((struct pic_proc *)(o).u.data)
 
 #define pic_proc_cfunc_p(o) (pic_proc_ptr(o)->cfunc_p)
diff --git a/src/vm.c b/src/vm.c
index 1dc31bf7..1e2bb2b3 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -224,6 +224,10 @@ pic_run(pic_state *pic, struct pic_proc *proc, pic_value args)
       struct pic_proc *proc;
 
       c = pic->sp[-pc->u.i];
+      if (! pic_proc_p(c)) {
+	pic->errmsg = "invalid application";
+	goto L_RAISE;
+      }
       proc = pic_proc_ptr(c);
 
       ci = PUSHCI();