diff --git a/libsuicmez/suicmez_gc.c b/libsuicmez/suicmez_gc.c
index 84ea666..f51aa70 100644
--- a/libsuicmez/suicmez_gc.c
+++ b/libsuicmez/suicmez_gc.c
@@ -60,7 +60,9 @@ void gc_remove_root(void **slot) {
 void gc_write_barrier(void *owner, void *value) {
     if (is_old(owner) && is_young(value)) {
         size_t idx = card_index(owner);
-        gc.card_table[idx] = 1;
+        if (idx < gc.card_count){
+            gc.card_table[idx] = 1;
+        }
     }
 }
 
@@ -93,6 +95,7 @@ static Obj *forward(Obj *obj) {
     if (obj->header.age >= PROMOTION_AGE) {
         Obj *p = promote(obj);
         obj->header.forwarding = p;
+        scan_object_fields(p);
         return p;
     }
 
@@ -166,9 +169,13 @@ static void gc_minor_collect(void) {
 
 void *gc_alloc(const TypeInfo *type, size_t payload_size) {
     size_t size = sizeof(ObjHeader) + payload_size;
+    size = (size + sizeof(void*) - 1) & ~(sizeof(void*) - 1);
 
     if (gc.from_ptr + size > gc.from_space + gc.young_size) {
         gc_minor_collect();
+        if ((gc.old_ptr - gc.old) > (gc.old_size * 7 / 10)) {
+            gc_collect_old();
+        }
     }
 
     Obj *obj = (Obj*)gc.from_ptr;
@@ -210,6 +217,107 @@ void gc_init(void) {
     gc.root_count = 0;
 }
 
+static void mark_object_fields(Obj *obj) {
+    const TypeInfo *t = obj->header.type;
+    for (uint16_t i = 0; i < t->field_count; i++) {
+        if (t->pointer_bitmap[i]) {
+            Obj *child = (Obj*)obj->fields[i];
+            if (child && is_old(child)) {
+                mark_obj(child);
+            }
+        }
+    }
+}
+
+static void mark_obj(Obj *obj) {
+    if (!obj) return;
+    if (!(obj->header.flags & MARKED)) {
+        obj->header.flags |= MARKED;
+        mark_object_fields(obj);
+    }
+}
+
+static void mark_roots(void) {
+    for (size_t i = 0; i < gc.root_count; i++) {
+        Obj *obj = (Obj*)*gc.roots[i];
+        if (obj && is_old(obj)) {
+            mark_obj(obj);
+        }
+    }
+}
+
+static void compute_forwarding(void) {
+    uint8_t *dest = gc.old;
+    uint8_t *scan = gc.old;
+
+    while (scan < gc.old_ptr) {
+        Obj *obj = (Obj*)scan;
+        if (obj->header.flags & MARKED) {
+            obj->header.forwarding = (Obj*)dest;
+            dest += obj->header.size;
+        }
+        scan += obj->header.size;
+    }
+}
+
+static void update_old_pointers(void) {
+    uint8_t *scan = gc.old;
+
+    while (scan < gc.old_ptr) {
+        Obj *obj = (Obj*)scan;
+        if (obj->header.flags & MARKED) {
+            const TypeInfo *t = obj->header.type;
+            for (uint16_t i = 0; i < t->field_count; i++) {
+                if (t->pointer_bitmap[i]) {
+                    Obj *child = (Obj*)obj->fields[i];
+                    if (child && is_old(child)) {
+                        obj->fields[i] = child->header.forwarding;
+                    }
+                }
+            }
+        }
+        scan += obj->header.size;
+    }
+}
+
+static void update_root_pointers(void) {
+    for (size_t i = 0; i < gc.root_count; i++) {
+        Obj *obj = (Obj*)*gc.roots[i];
+        if (obj && is_old(obj)) {
+            *gc.roots[i] = obj->header.forwarding;
+        }
+    }
+}
+
+static void compact_old(void) {
+    uint8_t *scan = gc.old;
+    uint8_t *dest = gc.old;
+
+    while (scan < gc.old_ptr) {
+        Obj *obj = (Obj*)scan;
+        if (obj->header.flags & MARKED) {
+            Obj *new_loc = obj->header.forwarding;
+            memmove(new_loc, obj, obj->header.size);
+
+            Obj *moved = new_loc;
+            moved->header.flags &= ~MARKED;
+            moved->header.forwarding = NULL;
+
+            dest += moved->header.size;
+        }
+        scan += obj->header.size;
+    }
+
+    gc.old_ptr = dest;
+}
+
+void gc_collect_old(void) {
+    mark_roots();
+    compute_forwarding();
+    update_root_pointers();
+    update_old_pointers();
+    compact_old();
+}
 
 void gc_shutdown(void) {
     free(gc.from_space);