diff --git a/src/c/big.d b/src/c/big.d
index 6741138d7..1ed72e01f 100644
--- a/src/c/big.d
+++ b/src/c/big.d
@@ -282,22 +282,22 @@ _ecl_fix_divided_by_big(cl_fixnum x, cl_object y)
 static void *
 mp_alloc(size_t size)
 {
-        return ecl_alloc_atomic_align(size, sizeof(mp_limb_t));
-}
-
-static void *
-mp_realloc(void *ptr, size_t osize, size_t nsize)
-{
-        mp_limb_t *p = ecl_alloc_atomic_align(nsize, sizeof(mp_limb_t));
-        memcpy(p, ptr, (osize < nsize)? osize : nsize);
-        ecl_dealloc(ptr);
-        return p;
+        return ecl_alloc_uncollectable(size);
 }
 
 static void
 mp_free(void *ptr, size_t size)
 {
-        ecl_dealloc(ptr);
+        ecl_free_uncollectable(ptr);
+}
+
+static void *
+mp_realloc(void *ptr, size_t osize, size_t nsize)
+{
+        mp_limb_t *p = mp_alloc(nsize);
+        memcpy(p, ptr, (osize < nsize)? osize : nsize);
+        mp_free(ptr, osize);
+        return p;
 }
 
 cl_fixnum
diff --git a/src/c/number.d b/src/c/number.d
index d1144c93f..c55da4d49 100644
--- a/src/c/number.d
+++ b/src/c/number.d
@@ -234,6 +234,7 @@ ecl_to_uint64_t(cl_object x) {
                                 output = (ecl_uint64_t)mpz_get_ui(copy->big.big_num);
                                 output = (output << 32) +
                                         (ecl_uint64_t)mpz_get_ui(x->big.big_num);
+                                _ecl_big_register_free(copy);
                                 return output;
                         }
                 }