diff --git a/byterun/major_gc.c b/byterun/major_gc.c
index 15207e436..b33612105 100644
--- a/byterun/major_gc.c
+++ b/byterun/major_gc.c
@@ -87,21 +87,34 @@ static void mark_slice (work)
      long work;
 {
   value v, child;
-  mlsize_t i;
+  header_t hd;
+  mlsize_t size, i;
 
   while (work > 0){
     if (gray_vals_cur > gray_vals){
       v = *--gray_vals_cur;
-      Assert (Is_gray_val (v));
-      Hd_val (v) = Blackhd_hd (Hd_val (v));
-      if (Tag_val (v) < No_scan_tag){
-	for (i = Wosize_val (v); i > 0;){
-	  --i;
+      hd = Hd_val(v);
+      Assert (Is_gray_hd (hd));
+      Hd_val (v) = Blackhd_hd (hd);
+      size = Wosize_hd(hd);
+      if (Tag_hd (hd) < No_scan_tag){
+	for (i = 0; i < size; i++){
 	  child = Field (v, i);
-	  darken (child);
-	}
+          if (Is_block (child) && Is_in_heap (child)) {
+            hd = Hd_val(child);
+            if (Tag_hd(hd) == Infix_tag) {
+              child -= Infix_offset_val(child);
+              hd = Hd_val(child);
+            }
+            if (Is_white_hd (hd)){
+              Hd_val (child) = Grayhd_hd (hd);
+              *gray_vals_cur++ = child;
+              if (gray_vals_cur >= gray_vals_end) realloc_gray_vals ();
+            }
+          }
+        }
       }
-      work -= Whsize_val (v);
+      work -= Whsize_wosize(size);
     }else if (markhp != NULL){
       if (markhp == limit){
 	chunk = (((heap_chunk_head *) chunk) [-1]).next;
diff --git a/byterun/minor_gc.c b/byterun/minor_gc.c
index 2ee3359a9..1157e3262 100644
--- a/byterun/minor_gc.c
+++ b/byterun/minor_gc.c
@@ -52,39 +52,43 @@ void oldify (p, v)
      value *p;
      value v;
 {
-  value result;
-  mlsize_t i;
+  value result, field0;
+  header_t hd;
+  mlsize_t sz, i;
+  int tag;
 
  tail_call:
   if (Is_block (v) && Is_young (v)){
     Assert (Hp_val (v) >= young_ptr);
-    if (Is_blue_val (v)){    /* Already forwarded ? */
+    hd = Hd_val (v);
+    tag = Tag_hd (hd);
+    if (Is_blue_hd (hd)){    /* Already forwarded ? */
       *p = Field (v, 0);     /* Then the forward pointer is the first field. */
-    }else if (Tag_val(v) == Infix_tag) {
-      mlsize_t offset = Infix_offset_val(v);
+    }else if (tag == Infix_tag) {
+      mlsize_t offset = Infix_offset_hd (hd);
       oldify(p, v - offset);
       *p += offset;
-    }else if (Tag_val (v) >= No_scan_tag){
-      result = alloc_shr (Wosize_val (v), Tag_val (v));
-      bcopy (Bp_val (v), Bp_val (result), Bosize_val (v));
-      Hd_val (v) = Bluehd_hd (Hd_val (v));    /* Put the forward flag. */
+    }else if (tag >= No_scan_tag){
+      sz = Wosize_hd (hd);
+      result = alloc_shr (sz, tag);
+      for (i = 0; i < sz; i++) Field(result, i) = Field(v, i);
+      Hd_val (v) = Bluehd_hd (hd);            /* Put the forward flag. */
       Field (v, 0) = result;                  /* And the forward pointer. */
       *p = result;
     }else{
       /* We can do recursive calls before all the fields are filled, because
          we will not be calling the major GC. */
-      value field0 = Field (v, 0);
-      mlsize_t sz = Wosize_val (v);
-
-      result = alloc_shr (sz, Tag_val (v));
+      sz = Wosize_hd (hd);
+      result = alloc_shr (sz, tag);
       *p = result;
-      Hd_val (v) = Bluehd_hd (Hd_val (v));    /* Put the forward flag. */
+      field0 = Field (v, 0);
+      Hd_val (v) = Bluehd_hd (hd);            /* Put the forward flag. */
       Field (v, 0) = result;                  /* And the forward pointer. */
-      if (sz == 1){
+      if (sz == 1) {
         p = &Field (result, 0);
         v = field0;
         goto tail_call;
-      }else{
+      } else {
         oldify (&Field (result, 0), field0);
         for (i = 1; i < sz - 1; i++){
           oldify (&Field (result, i), Field (v, i));