diff --git a/src/mzscheme/src/jit.c b/src/mzscheme/src/jit.c
index 4fbdaa5794..581e89e6e5 100644
--- a/src/mzscheme/src/jit.c
+++ b/src/mzscheme/src/jit.c
@@ -107,6 +107,7 @@ static void *call_original_binary_arith_for_branch_code;
 static void *call_original_binary_rev_arith_for_branch_code;
 static void *bad_car_code, *bad_cdr_code;
 static void *bad_caar_code, *bad_cdar_code, *bad_cadr_code, *bad_cddr_code;
+static void *bad_unbox_code;
 static void *vector_ref_code, *vector_ref_check_index_code, *vector_set_code, *vector_set_check_index_code;
 static void *string_ref_code, *string_ref_check_index_code, *string_set_code, *string_set_check_index_code;
 static void *bytes_ref_code, *bytes_ref_check_index_code, *bytes_set_code, *bytes_set_check_index_code;
@@ -2773,6 +2774,9 @@ static int generate_inlined_unary(mz_jit_state *jitter, Scheme_App2_Rec *app, in
   } else if (IS_NAMED_PRIM(rator, "vector?")) {
     generate_inlined_type_test(jitter, app, scheme_vector_type, scheme_vector_type, for_branch, branch_short);
     return 1;
+  } else if (IS_NAMED_PRIM(rator, "box?")) {
+    generate_inlined_type_test(jitter, app, scheme_box_type, scheme_box_type, for_branch, branch_short);
+    return 1;
   } else if (IS_NAMED_PRIM(rator, "string?")) {
     generate_inlined_type_test(jitter, app, scheme_char_string_type, scheme_char_string_type, for_branch, branch_short);
     return 1;
@@ -2862,6 +2866,34 @@ static int generate_inlined_unary(mz_jit_state *jitter, Scheme_App2_Rec *app, in
       }
       __END_SHORT_JUMPS__(1);
 
+      return 1;
+    } else if (IS_NAMED_PRIM(rator, "unbox")) {
+      GC_CAN_IGNORE jit_insn *reffail, *ref;
+
+      LOG_IT(("inlined unbox\n"));
+
+      mz_runstack_skipped(jitter, 1);
+
+      generate_non_tail(app->rand, jitter, 0, 1);
+      CHECK_LIMIT();
+
+      mz_runstack_unskipped(jitter, 1);
+
+      __START_SHORT_JUMPS__(1);
+      ref = jit_bmci_ul(jit_forward(), JIT_R0, 0x1);
+      __END_SHORT_JUMPS__(1);
+
+      reffail = _jit.x.pc;
+      (void)jit_jmpi(bad_unbox_code);
+
+      __START_SHORT_JUMPS__(1);
+      mz_patch_branch(ref);
+      jit_ldxi_s(JIT_R1, JIT_R0, &((Scheme_Object *)0x0)->type);
+      (void)jit_bnei_i(reffail, JIT_R1, scheme_box_type);
+      __END_SHORT_JUMPS__(1);
+
+      (void)jit_ldxi_p(JIT_R0, JIT_R0, &SCHEME_BOX_VAL(0x0));
+      
       return 1;
     } else if (IS_NAMED_PRIM(rator, "syntax-e")) {
       LOG_IT(("inlined syntax-e\n"));
@@ -4888,6 +4920,14 @@ static int do_generate_common(mz_jit_state *jitter, void *_data)
     CHECK_LIMIT();
   }
 
+  /* *** bad_unbox_code *** */
+  /* R0 is argument */
+  bad_unbox_code = jit_get_ip().ptr;
+  jit_prepare(1);
+  jit_pusharg_i(JIT_R0);
+  (void)mz_finish(scheme_unbox);
+  CHECK_LIMIT();
+
   /* *** call_original_unary_arith_code *** */
   /* R0 is arg, R2 is code pointer, V1 is return address */
   for (i = 0; i < 3; i++) {
diff --git a/src/mzscheme/src/list.c b/src/mzscheme/src/list.c
index 5d2f6833ff..e845f4fff0 100644
--- a/src/mzscheme/src/list.c
+++ b/src/mzscheme/src/list.c
@@ -402,16 +402,15 @@ scheme_init_list (Scheme_Env *env)
 						    "box-immutable",
 						    1, 1),
 			     env);
-  scheme_add_global_constant(BOXP,
-			     scheme_make_folding_prim(box_p,
-						      BOXP,
-						      1, 1, 1),
-			     env);
-  scheme_add_global_constant(UNBOX,
-			     scheme_make_noncm_prim(unbox,
-						    UNBOX,
-						    1, 1),
-			     env);
+  
+  p = scheme_make_folding_prim(box_p, BOXP, 1, 1, 1);
+  SCHEME_PRIM_PROC_FLAGS(p) |= SCHEME_PRIM_IS_UNARY_INLINED;  
+  scheme_add_global_constant(BOXP, p, env);
+
+  p = scheme_make_noncm_prim(unbox, UNBOX, 1, 1);
+  SCHEME_PRIM_PROC_FLAGS(p) |= SCHEME_PRIM_IS_UNARY_INLINED;  
+  scheme_add_global_constant(UNBOX, p, env);
+
   scheme_add_global_constant(SETBOX,
 			     scheme_make_noncm_prim(set_box,
 						    SETBOX,
diff --git a/src/mzscheme/src/stxobj.c b/src/mzscheme/src/stxobj.c
index 37020c63df..498076007b 100644
--- a/src/mzscheme/src/stxobj.c
+++ b/src/mzscheme/src/stxobj.c
@@ -72,6 +72,8 @@ static Scheme_Object *syntax_src_module(int argc, Scheme_Object **argv);
 
 static Scheme_Object *syntax_recertify(int argc, Scheme_Object **argv);
 
+static Scheme_Object *lift_inactive_certs(Scheme_Object *o, int as_active);
+
 static Scheme_Object *source_symbol; /* uninterned! */
 static Scheme_Object *share_symbol; /* uninterned! */
 static Scheme_Object *origin_symbol;
@@ -1514,7 +1516,10 @@ static void phase_shift_certs(Scheme_Object *o, Scheme_Object *owner_wraps, int
 	icerts = first;
     }
 
-    if (icerts) {
+    /* Even if icerts is NULL, preserve the pair in ->certs, 
+       to indicate no nested inactive certs. */
+
+    if (icerts || SCHEME_RPAIRP(((Scheme_Stx *)o)->certs)) {
       nc = scheme_make_raw_pair((Scheme_Object *)acerts, (Scheme_Object *)icerts);
     } else
       nc = (Scheme_Object *)acerts;
@@ -1911,6 +1916,7 @@ static int cert_in_chain(Scheme_Object *mark, Scheme_Object *key, Scheme_Cert *c
 }
 
 static Scheme_Object *add_certs(Scheme_Object *o, Scheme_Cert *certs, Scheme_Object *use_key, int active)
+/* If !active, then inactive certs must have been lifted already. */
 {
   Scheme_Cert *orig_certs, *cl, *now_certs, *next_certs;
   Scheme_Stx *stx = (Scheme_Stx *)o, *res;
@@ -1995,10 +2001,8 @@ static Scheme_Object *add_certs(Scheme_Object *o, Scheme_Cert *certs, Scheme_Obj
 Scheme_Object *scheme_stx_add_inactive_certs(Scheme_Object *o, Scheme_Object *certs)
   /* Also lifts existing inactive certs to the top. */
 {
-  if (!INACTIVE_CERTS((Scheme_Stx *)o)) {
-    /* Lift inactive certs*/
-    o = scheme_stx_activate_certs(o);
-  }
+  /* Lift inactive certs*/
+  o = lift_inactive_certs(o, 0);
 
   return add_certs(o, (Scheme_Cert *)certs, NULL, 0);
 }
@@ -2024,8 +2028,9 @@ Scheme_Object *scheme_stx_cert(Scheme_Object *o, Scheme_Object *mark, Scheme_Env
 	Also copy any certifications from plus_stx.
 	If active and mark is non-NULL, make inactive certificates active. */
 {
-  if (mark && active)
+  if (mark && active) {
     o = scheme_stx_activate_certs(o);
+  }
 
   if (plus_stx_or_certs) {
     Scheme_Cert *certs;
@@ -2033,11 +2038,16 @@ Scheme_Object *scheme_stx_cert(Scheme_Object *o, Scheme_Object *mark, Scheme_Env
       certs = ACTIVE_CERTS((Scheme_Stx *)plus_stx_or_certs);
     else
       certs = (Scheme_Cert *)plus_stx_or_certs;
-    if (certs)
+    if (certs) {
+      if (!active)
+        o = lift_inactive_certs(o, 0);
       o = add_certs(o, certs, key, active);
+    }
     /* Also copy over inactive certs, if any */
-    if (SCHEME_STXP(plus_stx_or_certs))
+    if (SCHEME_STXP(plus_stx_or_certs)) {
+      o = lift_inactive_certs(o, 0);
       o = add_certs(o, INACTIVE_CERTS((Scheme_Stx *)plus_stx_or_certs), key, 0);
+    }
   }
 
   if (menv && !menv->module->no_cert) {
@@ -2334,6 +2344,7 @@ static Scheme_Object *stx_activate_certs(Scheme_Object *o, Scheme_Cert **cp, Sch
       Scheme_Object *np;
       Scheme_Stx *res;
       Scheme_Cert *certs, *cc;
+
       res = (Scheme_Stx *)scheme_make_stx(stx->val, 
 					  stx->srcloc,
 					  stx->props);
@@ -2388,9 +2399,10 @@ static Scheme_Object *stx_activate_certs(Scheme_Object *o, Scheme_Cert **cp, Sch
       }
 
       o = stx_activate_certs(stx->val, cp, ht);
+
       if (!SAME_OBJ(o, stx->val)) {
 	Scheme_Stx *res;
-	res = (Scheme_Stx *)scheme_make_stx(stx->val, 
+	res = (Scheme_Stx *)scheme_make_stx(o, 
 					    stx->srcloc,
 					    stx->props);
 	res->wraps = stx->wraps;
@@ -2433,7 +2445,7 @@ static Scheme_Object *stx_activate_certs(Scheme_Object *o, Scheme_Cert **cp, Sch
     return o;
 }
 
-Scheme_Object *scheme_stx_activate_certs(Scheme_Object *o)
+static Scheme_Object *lift_inactive_certs(Scheme_Object *o, int as_active)
 {
   Scheme_Cert *certs = NULL;
   Scheme_Hash_Table *ht = NULL;
@@ -2442,7 +2454,7 @@ Scheme_Object *scheme_stx_activate_certs(Scheme_Object *o)
   if (!certs)
     return o;
 
-  o = add_certs(o, certs, NULL, 1);
+  o = add_certs(o, certs, NULL, as_active);
 
   if (ht)
     o = scheme_resolve_placeholders(o, 0);
@@ -2450,6 +2462,11 @@ Scheme_Object *scheme_stx_activate_certs(Scheme_Object *o)
   return o;
 }
 
+Scheme_Object *scheme_stx_activate_certs(Scheme_Object *o)
+{
+  return lift_inactive_certs(o, 1);
+}
+
 /*========================================================================*/
 /*                           stx comparison                               */
 /*========================================================================*/
@@ -5178,14 +5195,12 @@ Scheme_Object *scheme_datum_to_syntax(Scheme_Object *o,
     ((Scheme_Stx *)v)->props = ((Scheme_Stx *)stx_src)->props;
 
   if (copy_props && (copy_props != 1)) {
-    Scheme_Object *certs;
-    certs = ((Scheme_Stx *)stx_src)->certs;
-    /* To be on the safe side, drop a "definitely no inactive certs"
-       indication, if any: */
-    if (certs && SCHEME_PAIRP(certs) && !SCHEME_CDR(certs)) {
-      certs = SCHEME_CAR(certs);
+    if (ACTIVE_CERTS(((Scheme_Stx *)stx_src)))
+      v = add_certs(v, ACTIVE_CERTS((Scheme_Stx *)stx_src), NULL, 1);
+    if (INACTIVE_CERTS((Scheme_Stx *)stx_src)) {
+      v = lift_inactive_certs(v, 0);
+      v = add_certs(v, INACTIVE_CERTS((Scheme_Stx *)stx_src), NULL, 0);
     }
-    ((Scheme_Stx *)v)->certs = certs;
   }
 
   return v;
@@ -5396,7 +5411,6 @@ static Scheme_Object *syntax_to_datum(int argc, Scheme_Object **argv)
       return scheme_syntax_to_datum(argv[0], 1, scheme_make_hash_table(SCHEME_hash_ptr));
 #endif
 
-
   return scheme_syntax_to_datum(argv[0], 0, NULL);
 }
 
@@ -5494,8 +5508,8 @@ static Scheme_Object *datum_to_syntax(int argc, Scheme_Object **argv)
   }
 
   if (certs) {
-    certs = scheme_make_raw_pair(NULL, certs);
-    ((Scheme_Stx *)src)->certs = certs;
+    src = lift_inactive_certs(src, 0);
+    src = add_certs(src, (Scheme_Cert *)certs, NULL, 0);    
   }
 
   return src;
@@ -5978,6 +5992,9 @@ static Scheme_Object *syntax_recertify(int argc, Scheme_Object **argv)
       }
       
       if (!SAME_OBJ(orig_certs, new_certs)) {
+        if (i && !orig_certs)
+          stx = (Scheme_Stx *)lift_inactive_certs((Scheme_Object *)stx, 0);
+
 	res = (Scheme_Stx *)scheme_make_stx(stx->val, 
 					    stx->srcloc,
 					    stx->props);