diff --git a/extlib/benz/gc.c b/extlib/benz/gc.c
index d2849dc0..bf677583 100644
--- a/extlib/benz/gc.c
+++ b/extlib/benz/gc.c
@@ -533,6 +533,27 @@ gc_mark_global_symbols(pic_state *pic)
   M(uVALUES); M(uCALL_WITH_VALUES);
 }
 
+#define P(x) gc_mark(pic, pic->x)
+
+static void
+gc_mark_system_procedures(pic_state *pic)
+{
+  P(pCONS);
+  P(pCAR);
+  P(pCDR);
+  P(pNILP);
+  P(pSYMBOLP);
+  P(pPAIRP);
+  P(pNOT);
+  P(pADD);
+  P(pSUB);
+  P(pMUL);
+  P(pDIV);
+  P(pEQ);
+  P(pLT);
+  P(pLE);
+}
+
 static void
 gc_mark_phase(pic_state *pic)
 {
@@ -573,6 +594,9 @@ gc_mark_phase(pic_state *pic)
   /* mark reserved symbols */
   gc_mark_global_symbols(pic);
 
+  /* mark system procedures */
+  gc_mark_system_procedures(pic);
+
   /* global variables */
   if (pic->globals) {
     gc_mark_object(pic, (struct pic_object *)pic->globals);
diff --git a/extlib/benz/include/picrin.h b/extlib/benz/include/picrin.h
index 700d1a28..d5507f5d 100644
--- a/extlib/benz/include/picrin.h
+++ b/extlib/benz/include/picrin.h
@@ -106,6 +106,9 @@ struct pic_state {
   pic_sym *uADD, *uSUB, *uMUL, *uDIV, *uEQ, *uLT, *uLE, *uGT, *uGE, *uNOT;
   pic_sym *uVALUES, *uCALL_WITH_VALUES;
 
+  pic_value pCONS, pCAR, pCDR, pNILP, pPAIRP, pSYMBOLP, pNOT;
+  pic_value pADD, pSUB, pMUL, pDIV, pEQ, pLT, pLE;
+
   struct pic_lib *PICRIN_BASE;
   struct pic_lib *PICRIN_USER;
 
diff --git a/extlib/benz/state.c b/extlib/benz/state.c
index c06474f1..3c74a25a 100644
--- a/extlib/benz/state.c
+++ b/extlib/benz/state.c
@@ -118,6 +118,9 @@ pic_features(pic_state *pic)
 #define VM(uid, name)                                                   \
   pic_define_syntactic_keyword_(pic, pic->lib->env, pic_intern_cstr(pic, name), uid)
 
+#define VM2(proc, name)                         \
+  proc = pic_ref(pic, pic->lib, name)
+
 static void
 pic_init_core(pic_state *pic)
 {
@@ -177,6 +180,21 @@ pic_init_core(pic_state *pic)
     pic_init_attr(pic); DONE;
     pic_init_reg(pic); DONE;
 
+    VM2(pic->pCONS, "cons");
+    VM2(pic->pCAR, "car");
+    VM2(pic->pCDR, "cdr");
+    VM2(pic->pNILP, "null?");
+    VM2(pic->pSYMBOLP, "symbol?");
+    VM2(pic->pPAIRP, "pair?");
+    VM2(pic->pNOT, "not");
+    VM2(pic->pADD, "+");
+    VM2(pic->pSUB, "-");
+    VM2(pic->pMUL, "*");
+    VM2(pic->pDIV, "/");
+    VM2(pic->pEQ, "=");
+    VM2(pic->pLT, "<");
+    VM2(pic->pLE, "<=");
+
     pic_try {
       pic_load_cstr(pic, &pic_boot[0][0]);
     }
@@ -354,6 +372,22 @@ pic_open(pic_allocf allocf, void *userdata)
   U(uCALL_WITH_VALUES, "call-with-values");
   pic_gc_arena_restore(pic, ai);
 
+  /* system procedures */
+  pic->pCONS = pic_invalid_value();
+  pic->pCAR = pic_invalid_value();
+  pic->pCDR = pic_invalid_value();
+  pic->pNILP = pic_invalid_value();
+  pic->pSYMBOLP = pic_invalid_value();
+  pic->pPAIRP = pic_invalid_value();
+  pic->pNOT = pic_invalid_value();
+  pic->pADD = pic_invalid_value();
+  pic->pSUB = pic_invalid_value();
+  pic->pMUL = pic_invalid_value();
+  pic->pDIV = pic_invalid_value();
+  pic->pEQ = pic_invalid_value();
+  pic->pLT = pic_invalid_value();
+  pic->pLE = pic_invalid_value();
+
   /* root tables */
   pic->globals = pic_make_dict(pic);
   pic->macros = pic_make_dict(pic);
diff --git a/extlib/benz/vm.c b/extlib/benz/vm.c
index 79fa5aa2..07ee2099 100644
--- a/extlib/benz/vm.c
+++ b/extlib/benz/vm.c
@@ -839,15 +839,16 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
       NEXT;
     }
 
-#define check_args(name, n) do {                \
-      if (c.u.i != n + 1) {                     \
-        goto L_CALL;                            \
-      }                                         \
+#define check_condition(name, n) do {                                   \
+      if (! pic_eq_p(pic->p##name, pic_dict_ref(pic, pic->globals, pic->u##name))) \
+        goto L_CALL;                                                    \
+      if (c.u.i != n + 1)                                               \
+        goto L_CALL;                                                    \
     } while (0)
 
     CASE(OP_CONS) {
       pic_value a, b;
-      check_args("cons", 2);
+      check_condition(CONS, 2);
       pic_gc_protect(pic, b = POP());
       pic_gc_protect(pic, a = POP());
       (void)POP();
@@ -857,7 +858,7 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
     }
     CASE(OP_CAR) {
       pic_value p;
-      check_args("car", 1);
+      check_condition(CAR, 1);
       p = POP();
       (void)POP();
       PUSH(pic_car(pic, p));
@@ -865,7 +866,7 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
     }
     CASE(OP_CDR) {
       pic_value p;
-      check_args("cdr", 1);
+      check_condition(CDR, 1);
       p = POP();
       (void)POP();
       PUSH(pic_cdr(pic, p));
@@ -873,7 +874,7 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
     }
     CASE(OP_NILP) {
       pic_value p;
-      check_args("null?", 1);
+      check_condition(NILP, 1);
       p = POP();
       (void)POP();
       PUSH(pic_bool_value(pic_nil_p(p)));
@@ -881,7 +882,7 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
     }
     CASE(OP_SYMBOLP) {
       pic_value p;
-      check_args("symbol?", 1);
+      check_condition(SYMBOLP, 1);
       p = POP();
       (void)POP();
       PUSH(pic_bool_value(pic_sym_p(p)));
@@ -889,7 +890,7 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
     }
     CASE(OP_PAIRP) {
       pic_value p;
-      check_args("pair?", 1);
+      check_condition(PAIRP, 1);
       p = POP();
       (void)POP();
       PUSH(pic_bool_value(pic_pair_p(p)));
@@ -897,7 +898,7 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
     }
     CASE(OP_NOT) {
       pic_value v;
-      check_args("not", 1);
+      check_condition(NOT, 1);
       v = pic_false_p(POP()) ? pic_true_value() : pic_false_value();
       (void)POP();
       PUSH(v);
@@ -906,7 +907,7 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
 
     CASE(OP_ADD) {
       pic_value a, b;
-      check_args("+", 2);
+      check_condition(ADD, 2);
       b = POP();
       a = POP();
       (void)POP();
@@ -915,7 +916,7 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
     }
     CASE(OP_SUB) {
       pic_value a, b;
-      check_args("-", 2);
+      check_condition(SUB, 2);
       b = POP();
       a = POP();
       (void)POP();
@@ -924,7 +925,7 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
     }
     CASE(OP_MUL) {
       pic_value a, b;
-      check_args("*", 2);
+      check_condition(MUL, 2);
       b = POP();
       a = POP();
       (void)POP();
@@ -933,7 +934,7 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
     }
     CASE(OP_DIV) {
       pic_value a, b;
-      check_args("/", 2);
+      check_condition(DIV, 2);
       b = POP();
       a = POP();
       (void)POP();
@@ -942,7 +943,7 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
     }
     CASE(OP_EQ) {
       pic_value a, b;
-      check_args("=", 2);
+      check_condition(EQ, 2);
       b = POP();
       a = POP();
       (void)POP();
@@ -951,7 +952,7 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
     }
     CASE(OP_LE) {
       pic_value a, b;
-      check_args("<", 2);
+      check_condition(LT, 2);
       b = POP();
       a = POP();
       (void)POP();
@@ -960,7 +961,7 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
     }
     CASE(OP_LT) {
       pic_value a, b;
-      check_args("<=", 2);
+      check_condition(LE, 2);
       b = POP();
       a = POP();
       (void)POP();
diff --git a/t/override.scm b/t/override.scm
new file mode 100644
index 00000000..92d296f7
--- /dev/null
+++ b/t/override.scm
@@ -0,0 +1,13 @@
+(import (picrin base)
+        (picrin test))
+
+(test-begin)
+
+(define orig-cons cons)
+
+(set! symbol? list)
+
+(test '(1)
+      (symbol? 1))
+
+(test-end)