diff --git a/allchblk.c b/allchblk.c
index 22e298e0a..8601018ae 100644
--- a/allchblk.c
+++ b/allchblk.c
@@ -1043,7 +1043,11 @@ GC_INNER void GC_freehblk(struct hblk *hbp)
       /* space at once.  If we don't catch it here, strange things happen   */
       /* later.                                                             */
 
+    // Clear all the mark bytes to prevent blocks from lingering as
+    // uncollectable. Instead, this should only be opted-in on each allocation.
+    BZERO(hhdr->hb_marks, sizeof(hhdr->hb_marks));
     GC_remove_counts(hbp, (size_t)size);
+
     hhdr -> hb_sz = size;
 #   ifdef USE_MUNMAP
       hhdr -> hb_last_reclaimed = (unsigned short)GC_gc_no;
diff --git a/include/private/gc_pmark.h b/include/private/gc_pmark.h
index 7be3406f3..22bc05e95 100644
--- a/include/private/gc_pmark.h
+++ b/include/private/gc_pmark.h
@@ -153,7 +153,7 @@ GC_INLINE mse * GC_push_obj(ptr_t obj, const hdr * hhdr, mse * mark_stack_top,
       { /* cannot use do-while(0) here */ \
         char * mark_byte_addr = (char *)(hhdr)->hb_marks + (bit_no); \
         if (*mark_byte_addr != 0) break; /* go to the enclosing loop end */ \
-        *mark_byte_addr = 1; \
+        *mark_byte_addr |= MARK_TAG; \
       }
 # endif /* !PARALLEL_MARK */
 #else
diff --git a/malloc.c b/malloc.c
index 5b56742fc..c1196b2d6 100644
--- a/malloc.c
+++ b/malloc.c
@@ -315,7 +315,10 @@ GC_INNER void * GC_generic_malloc_aligned(size_t lb, int k, unsigned flags,
 
 GC_API GC_ATTR_MALLOC void * GC_CALL GC_generic_malloc(size_t lb, int k)
 {
-    return GC_generic_malloc_aligned(lb, k, 0 /* flags */, 0 /* align_m1 */);
+    void* ptr =  GC_generic_malloc_aligned(lb, k, 0 /* flags */, 0 /* align_m1 */);
+    if (ptr)
+      GC_clear_uncollectable(ptr);
+    return ptr;
 }
 
 GC_API GC_ATTR_MALLOC void * GC_CALL GC_malloc_kind_global(size_t lb, int k)
@@ -451,7 +454,14 @@ GC_API GC_ATTR_MALLOC void * GC_CALL GC_generic_malloc_uncollectable(
 /* Allocate lb bytes of pointerful, traced, but not collectible data.   */
 GC_API GC_ATTR_MALLOC void * GC_CALL GC_malloc_uncollectable(size_t lb)
 {
+#ifdef FINALIZER_ELISION
+  void* ptr = GC_generic_malloc(lb, NORMAL);
+  if (ptr)
+    GC_set_uncollectable(ptr);
+  return ptr;
+#else
   return GC_generic_malloc_uncollectable(lb, UNCOLLECTABLE);
+#endif
 }
 
 #ifdef GC_ATOMIC_UNCOLLECTABLE
@@ -667,8 +677,10 @@ GC_API void GC_CALL GC_free(void * p)
         if (EXPECT(NULL == hhdr, FALSE)) return;
 #   endif
     GC_ASSERT(GC_base(p) == p);
+    GC_ASSERT(GC_is_uncollectable(p));
     LOCK();
     free_internal(p, hhdr);
+
     FREE_PROFILER_HOOK(p);
     UNLOCK();
 }
diff --git a/mallocx.c b/mallocx.c
index 0481d93af..491e5010b 100644
--- a/mallocx.c
+++ b/mallocx.c
@@ -165,6 +165,8 @@ GC_API void * GC_CALL GC_realloc(void * p, size_t lb)
     }
     result = GC_generic_or_special_malloc((word)lb, obj_kind);
     if (EXPECT(result != NULL, TRUE)) {
+      if(GC_is_uncollectable(p))
+        GC_set_uncollectable(result);
       /* In case of shrink, it could also return original object.       */
       /* But this gives the client warning of imminent disaster.        */
       BCOPY(p, result, sz);
diff --git a/mark.c b/mark.c
index 8bb8b70f1..63efe09c1 100644
--- a/mark.c
+++ b/mark.c
@@ -187,8 +187,13 @@ GC_INNER void GC_clear_hdr_marks(hdr *hhdr)
     /* No race as GC_realloc holds the allocator lock while updating hb_sz. */
     last_bit = FINAL_MARK_BIT((size_t)hhdr->hb_sz);
 # endif
+    unsigned i;
+    size_t sz = (size_t)hhdr->hb_sz;
+    unsigned n_marks = (unsigned)FINAL_MARK_BIT(sz);
 
-    BZERO(hhdr -> hb_marks, sizeof(hhdr->hb_marks));
+    for (i = 0; i <= n_marks; i += (unsigned)MARK_BIT_OFFSET(sz)) {
+        hhdr -> hb_marks[i] &= ~MARK_TAG;
+    }
     set_mark_bit_from_hdr(hhdr, last_bit);
     hhdr -> hb_n_marks = 0;
 }
diff --git a/reclaim.c b/reclaim.c
index 93c0f9123..acc167833 100644
--- a/reclaim.c
+++ b/reclaim.c
@@ -201,12 +201,13 @@ STATIC ptr_t GC_reclaim_clear(struct hblk *hbp, const hdr *hhdr, word sz,
     p = hbp -> hb_body;
     plim = p + HBLKSIZE - sz;
     for (bit_no = 0; ADDR_GE(plim, p); bit_no += MARK_BIT_OFFSET(sz)) {
-        if (mark_bit_from_hdr(hhdr, bit_no)) {
+        if (mark_bit_from_hdr(hhdr, bit_no) || uncollectable_bit_from_hdr(hhdr, bit_no)) {
             p += sz;
         } else {
             /* The object is available - put it on list. */
             obj_link(p) = list;
             list = p;
+            clear_uncollectable_bit_from_hdr(HDR(p), bit_no);
             FREE_PROFILER_HOOK(p);
             p = (ptr_t)GC_clear_block((word *)p, sz, pcount);
         }
@@ -231,11 +232,12 @@ STATIC ptr_t GC_reclaim_uninit(struct hblk *hbp, const hdr *hhdr, word sz,
     plim = (ptr_t)hbp + HBLKSIZE - sz;
     for (bit_no = 0; ADDR_GE(plim, p);
          bit_no += MARK_BIT_OFFSET(sz), p += sz) {
-        if (!mark_bit_from_hdr(hhdr, bit_no)) {
+        if (!mark_bit_from_hdr(hhdr, bit_no) && !uncollectable_bit_from_hdr(hhdr, bit_no)) {
             n_bytes_found += sz;
             /* The object is available - put it on list. */
             obj_link(p) = list;
             list = p;
+            clear_uncollectable_bit_from_hdr(HDR(p), bit_no);
             FREE_PROFILER_HOOK(p);
         }
     }
@@ -293,7 +295,7 @@ STATIC void GC_reclaim_check(struct hblk *hbp, const hdr *hhdr, word sz)
     plim = p + HBLKSIZE - sz;
     for (bit_no = 0; ADDR_GE(plim, p);
          bit_no += MARK_BIT_OFFSET(sz), p += sz) {
-      if (!mark_bit_from_hdr(hhdr, bit_no))
+      if (!mark_bit_from_hdr(hhdr, bit_no) && !uncollectable_bit_from_hdr(hhdr, bit_no))
         GC_add_leaked(p);
     }
 }
@@ -866,7 +868,7 @@ STATIC void GC_CALLBACK GC_do_enumerate_reachable_objects(struct hblk *hbp,
   }
   /* Go through all objects in the block. */
   for (bit_no = 0; ADDR_GE(plim, p); bit_no += MARK_BIT_OFFSET(sz), p += sz) {
-    if (mark_bit_from_hdr(hhdr, bit_no)) {
+    if (mark_bit_from_hdr(hhdr, bit_no) || uncollectable_bit_from_hdr(hhdr, bit_no)) {
       ((struct enumerate_reachable_s *)ped)->proc(p, sz,
                         ((struct enumerate_reachable_s *)ped)->client_data);
     }