diff --git a/default.nix b/default.nix
index 9ac6e7c2..3a9b4466 100644
--- a/default.nix
+++ b/default.nix
@@ -141,6 +141,7 @@ let
             xo-arena          = self.callPackage pkgs/xo-arena.nix          { buildDocs = true; };
             xo-facet          = self.callPackage pkgs/xo-facet.nix          {};
             xo-allocutil      = self.callPackage pkgs/xo-allocutil.nix      {};
+            xo-alloc          = self.callPackage pkgs/xo-alloc.nix          {}; # buildDocs = true;
             xo-refcnt         = self.callPackage pkgs/xo-refcnt.nix         {};
             xo-ordinaltree    = self.callPackage pkgs/xo-ordinaltree.nix    {};
             xo-flatstring     = self.callPackage pkgs/xo-flatstring.nix     { buildDocs = true; buildExamples = true; };
@@ -479,13 +480,14 @@ in
   pkgs = pkgs;
   xo = {
     cmake          = pkgs.xo-cmake;
-#    facet          = pkgs.xo-facet;
     indentlog      = pkgs.xo-indentlog;
     refcnt         = pkgs.xo-refcnt;
     subsys         = pkgs.xo-subsys;
     randomgen      = pkgs.xo-randomgen;
     arena          = pkgs.xo-arena;
     facet          = pkgs.xo-facet;
+    allocutil      = pkgs.xo-allocutil;
+    alloc          = pkgs.xo-alloc;
     ordinaltree    = pkgs.xo-ordinaltree;
     flatstring     = pkgs.xo-flatstring;
     pyutil         = pkgs.xo-pyutil;
diff --git a/pkgs/xo-alloc.nix b/pkgs/xo-alloc.nix
new file mode 100644
index 00000000..51cbda83
--- /dev/null
+++ b/pkgs/xo-alloc.nix
@@ -0,0 +1,64 @@
+{
+  # nixpkgs dependencies
+  lib, stdenv, cmake, catch2,
+  doxygen,
+
+  python3Packages,
+
+  sphinx, graphviz,
+
+  # xo dependencies
+  xo-callback,
+  xo-unit,
+  xo-reflect,
+#  xo-randomgen,
+  xo-reflectutil,
+  xo-indentlog,
+  xo-allocutil,
+  xo-cmake,
+
+  buildDocs ? false,
+  doCheck ? true,
+} :
+
+stdenv.mkDerivation (finalattrs:
+  {
+    name = "xo-alloc";
+
+    src = ../xo-alloc;
+
+    cmakeFlags = ["-DCMAKE_MODULE_PATH=${xo-cmake}/share/cmake"]
+                  ++ lib.optionals buildDocs ["-DXO_ENABLE_DOCS=on"]
+                  ++ ["-DENABLE_TESTING=1"];
+
+    inherit buildDocs;
+    inherit doCheck;
+
+    postBuild = lib.optionalString buildDocs ''
+      cmake --build . -- docs
+    '';
+
+    nativeBuildInputs = [
+      cmake
+      catch2
+      xo-cmake
+#      xo-randomgen
+    ] ++ lib.optionals buildDocs [
+      doxygen
+      sphinx
+      graphviz
+      python3Packages.sphinx-rtd-theme
+      python3Packages.breathe
+      python3Packages.sphinxcontrib-ditaa
+      python3Packages.sphinxcontrib-plantuml
+      python3Packages.pillow
+    ];
+    propagatedBuildInputs = [
+      xo-callback
+      xo-unit
+      xo-reflect
+      xo-allocutil
+      xo-reflectutil
+      xo-indentlog
+    ];
+  })
diff --git a/pkgs/xo-allocutil.nix b/pkgs/xo-allocutil.nix
index acdceb1e..dd66dbd6 100644
--- a/pkgs/xo-allocutil.nix
+++ b/pkgs/xo-allocutil.nix
@@ -3,6 +3,7 @@
   stdenv, cmake, catch2,
 
   # xo dependencies
+  xo-allocutil,
   xo-cmake,
 #  xo-randomgen,
 #  xo-reflectutil,
diff --git a/xo-alloc/src/alloc/ArenaAlloc.cpp b/xo-alloc/src/alloc/ArenaAlloc.cpp
index d7f794f3..dc80eb4e 100644
--- a/xo-alloc/src/alloc/ArenaAlloc.cpp
+++ b/xo-alloc/src/alloc/ArenaAlloc.cpp
@@ -390,8 +390,10 @@ namespace xo {
 
             /* word size for alignment */
             constexpr uint32_t c_bpw = sizeof(std::uintptr_t);
+            (void)c_bpw;
 
             std::uintptr_t free_u64 = reinterpret_cast<std::uintptr_t>(free_ptr_);
+            (void)free_u64;
 
             assert(free_u64 % c_bpw == 0ul);
 
diff --git a/xo-alloc/src/alloc/GC.cpp b/xo-alloc/src/alloc/GC.cpp
index dd17fd3b..f1c52d1b 100644
--- a/xo-alloc/src/alloc/GC.cpp
+++ b/xo-alloc/src/alloc/GC.cpp
@@ -551,7 +551,7 @@ namespace xo {
                 case generation_result::nursery:
                     if (is_before_checkpoint(parent)) {
                         log && log(xtag("act", "N1->N0 must mlog"));
-                        
+
                         // N1->N0, so must log
                         this->mutation_log_[role2int(role::to_space)]->push_back(MutationLogEntry(parent, lhs));
                         ++(this->gc_statistics_.n_logged_mutation_);
@@ -974,12 +974,14 @@ namespace xo {
 
                                 from_entry.fixup_parent_child_moved(child_to);
 
+#ifndef NDEBUG
                                 {
                                     // verify fixup was effective
                                     IObject * child_from2 = from_entry.child();
                                     assert(child_from2 == child_to);
                                 }
-                                
+#endif
+
 
                                 // P->C', loc(C') in {N1', T'}