diff --git a/src/CHANGELOG b/src/CHANGELOG
index 9f93be6a5..0a754be24 100644
--- a/src/CHANGELOG
+++ b/src/CHANGELOG
@@ -24,6 +24,11 @@ ECL 9.9.1:
    macros and functions. Have a look at the end of src/h/external.h to see
    what functions are deprecated on each release -- typically they are functions
    that have been renamed with one of the prefixes, ecl_, cl_, si_, ext_ or _ecl.
+
+ - Bignums are now allocated as a compact IMMUTABLE unit that combines the lisp
+   object and the data for the GMP integer itself. Since it can be now
+   allocated as an atomic (i.e. pointerless) region of memory, the garbage
+   collector has to work less for marking and collecting them.
    
 
 ;;; Local Variables: ***
diff --git a/src/c/big.d b/src/c/big.d
index c30ffee91..db85f45fc 100644
--- a/src/c/big.d
+++ b/src/c/big.d
@@ -34,14 +34,20 @@ _ecl_big_register_free(cl_object x)
 static cl_object
 _ecl_big_copy(cl_object old)
 {
+        cl_fixnum size = old->big.big_size;
+        cl_index dim = (size < 0)? (-size) : size;
+        cl_index bytes = dim * sizeof(mp_limb_t);
+#ifdef GBC_BOEHM
+        char *data = ecl_alloc_atomic(bytes + sizeof(struct ecl_bignum));
+        cl_object new_big = (cl_object)data;
+        new_big->big.t = t_bignum;
+        new_big->big.big_limbs = ((char *)new_big) + sizeof(struct ecl_bignum);
+#else
 	cl_object new_big = ecl_alloc_object(t_bignum);
-        cl_fixnum dim, bytes;
-        dim = old->big.big_size;
-        new_big->big.big_size = dim;
-        if (dim < 0) dim = - dim;
-        new_big->big.big_dim = dim;
-        bytes = dim * sizeof(mp_limb_t);
         new_big->big.big_limbs = ecl_alloc_atomic(bytes);
+#endif
+        new_big->big.big_size = size;
+        new_big->big.big_dim = dim;
         memcpy(new_big->big.big_limbs, old->big.big_limbs, bytes);
         return new_big;
 }