diff --git a/gc/default/default.c b/gc/default/default.c
index a6572b6f4d7ceb..90232c76184a55 100644
--- a/gc/default/default.c
+++ b/gc/default/default.c
@@ -858,15 +858,15 @@ heap_page_in_global_empty_pages_pool(rb_objspace_t *objspace, struct heap_page *
 #define GET_HEAP_WB_UNPROTECTED_BITS(x) (&GET_HEAP_PAGE(x)->wb_unprotected_bits[0])
 #define GET_HEAP_MARKING_BITS(x)        (&GET_HEAP_PAGE(x)->marking_bits[0])
 
-
-#define RVALUE_AGE_BITMAP_INDEX(n)  (NUM_IN_PAGE(n) / (BITS_BITLENGTH / RVALUE_AGE_BIT_COUNT))
-#define RVALUE_AGE_BITMAP_OFFSET(n) ((NUM_IN_PAGE(n) % (BITS_BITLENGTH / RVALUE_AGE_BIT_COUNT)) * RVALUE_AGE_BIT_COUNT)
-
 static int
 RVALUE_AGE_GET(VALUE obj)
 {
     bits_t *age_bits = GET_HEAP_PAGE(obj)->age_bits;
-    return (int)(age_bits[RVALUE_AGE_BITMAP_INDEX(obj)] >> RVALUE_AGE_BITMAP_OFFSET(obj)) & RVALUE_AGE_BIT_MASK;
+    int idx = BITMAP_INDEX(obj) * 2;
+    int shift = BITMAP_OFFSET(obj);
+    int lo = (age_bits[idx] >> shift) & 1;
+    int hi = (age_bits[idx + 1] >> shift) & 1;
+    return lo | (hi << 1);
 }
 
 static void
@@ -874,10 +874,12 @@ RVALUE_AGE_SET_BITMAP(VALUE obj, int age)
 {
     RUBY_ASSERT(age <= RVALUE_OLD_AGE);
     bits_t *age_bits = GET_HEAP_PAGE(obj)->age_bits;
-    // clear the bits
-    age_bits[RVALUE_AGE_BITMAP_INDEX(obj)] &= ~(RVALUE_AGE_BIT_MASK << (RVALUE_AGE_BITMAP_OFFSET(obj)));
-    // shift the correct value in
-    age_bits[RVALUE_AGE_BITMAP_INDEX(obj)] |= ((bits_t)age << RVALUE_AGE_BITMAP_OFFSET(obj));
+    int idx = BITMAP_INDEX(obj) * 2;
+    int shift = BITMAP_OFFSET(obj);
+    bits_t mask = (bits_t)1 << shift;
+
+    age_bits[idx]     = (age_bits[idx]     & ~mask) | ((bits_t)(age & 1) << shift);
+    age_bits[idx + 1] = (age_bits[idx + 1] & ~mask) | ((bits_t)((age >> 1) & 1) << shift);
 }
 
 static void
@@ -3508,7 +3510,6 @@ gc_sweep_plane(rb_objspace_t *objspace, rb_heap_t *heap, uintptr_t p, bits_t bit
                 }
                 gc_report(3, objspace, "page_sweep: %s is added to freelist\n", rb_obj_info(vp));
                 ctx->empty_slots++;
-                RVALUE_AGE_SET_BITMAP(vp, 0);
                 heap_page_add_freeobj(objspace, sweep_page, vp);
                 break;
               case T_ZOMBIE:
@@ -3525,7 +3526,6 @@ gc_sweep_plane(rb_objspace_t *objspace, rb_heap_t *heap, uintptr_t p, bits_t bit
                     if (RVALUE_REMEMBERED(objspace, vp)) rb_bug("page_sweep: %p - remembered.", (void *)p);
                 }
 #endif
-                if (RVALUE_WB_UNPROTECTED(objspace, vp)) CLEAR_IN_BITMAP(GET_HEAP_WB_UNPROTECTED_BITS(vp), vp);
 
 #if RGENGC_CHECK_MODE
 #define CHECK(x) if (x(objspace, vp) != FALSE) rb_bug("obj_free: " #x "(%s) != FALSE", rb_obj_info(vp))
@@ -3542,7 +3542,6 @@ gc_sweep_plane(rb_objspace_t *objspace, rb_heap_t *heap, uintptr_t p, bits_t bit
                     }
 
                     (void)VALGRIND_MAKE_MEM_UNDEFINED((void*)p, BASE_SLOT_SIZE);
-                    RVALUE_AGE_SET_BITMAP(vp, 0);
                     heap_page_add_freeobj(objspace, sweep_page, vp);
                     gc_report(3, objspace, "page_sweep: %s (fast path) added to freelist\n", rb_obj_info(vp));
                     ctx->freed_slots++;
@@ -3555,7 +3554,6 @@ gc_sweep_plane(rb_objspace_t *objspace, rb_heap_t *heap, uintptr_t p, bits_t bit
                     rb_gc_obj_free_vm_weak_references(vp);
                     if (rb_gc_obj_free(objspace, vp)) {
                         (void)VALGRIND_MAKE_MEM_UNDEFINED((void*)p, BASE_SLOT_SIZE);
-                        RVALUE_AGE_SET_BITMAP(vp, 0);
                         heap_page_add_freeobj(objspace, sweep_page, vp);
                         gc_report(3, objspace, "page_sweep: %s is added to freelist\n", rb_obj_info(vp));
                         ctx->freed_slots++;
@@ -3609,6 +3607,18 @@ gc_sweep_page(rb_objspace_t *objspace, rb_heap_t *heap, struct gc_sweep_context
 
     bits_t slot_mask = heap->slot_bits_mask;
 
+    // Clear wb_unprotected and age bits for all unmarked slots
+    {
+        bits_t *wb_unprotected_bits = sweep_page->wb_unprotected_bits;
+        bits_t *age_bits = sweep_page->age_bits;
+        for (int i = 0; i < bitmap_plane_count; i++) {
+            bits_t unmarked = ~bits[i] & slot_mask;
+            wb_unprotected_bits[i] &= ~unmarked;
+            age_bits[i * 2] &= ~unmarked;
+            age_bits[i * 2 + 1] &= ~unmarked;
+        }
+    }
+
     // Skip out of range slots at the head of the page
     bitset = ~bits[0];
     bitset >>= NUM_IN_PAGE(p);
diff --git a/zjit/src/backend/x86_64/mod.rs b/zjit/src/backend/x86_64/mod.rs
index d55dce1b9b82e0..138df69008fe2c 100644
--- a/zjit/src/backend/x86_64/mod.rs
+++ b/zjit/src/backend/x86_64/mod.rs
@@ -421,7 +421,7 @@ impl Assembler {
             }
         }
 
-        /// If a given operand is Opnd::Mem and it uses MemBase::Stack, lower it to MemBase::Reg using a scratch regsiter.
+        /// If a given operand is Opnd::Mem and it uses MemBase::Stack, lower it to MemBase::Reg using a scratch register.
         fn split_stack_membase(asm: &mut Assembler, opnd: Opnd, scratch_opnd: Opnd, stack_state: &StackState) -> Opnd {
             if let Opnd::Mem(Mem { base: stack_membase @ MemBase::Stack { .. }, disp, num_bits }) = opnd {
                 let base = Opnd::Mem(stack_state.stack_membase_to_mem(stack_membase));