diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 5abb327d93..44e1f10073 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -34,6 +34,7 @@ option(JEMALLOC           "JEMALLOC"           OFF)
 option(JSON               "JSON"               ON)
 # When OFF we disable LLVM support
 option(LLVM               "LLVM"               OFF)
+option(COMPRESSED_OBJECT_HEADER "COMPRESSED_OBJECT_HEARDER" ON)
 
 # When cross-compiling, we do not compile the standard library since
 # the executable will not work on the host machine
@@ -129,6 +130,25 @@ if ("${SMALL_ALLOCATOR}" MATCHES "ON")
   set(LEAN_SMALL_ALLOCATOR "#define LEAN_SMALL_ALLOCATOR")
 endif()
 
+if(CMAKE_SIZEOF_VOID_P EQUAL 8)
+  message(STATUS "64-bit machine detected")
+  set(NumBits 64)
+else()
+  message(STATUS "32-bit machine detected")
+  set(NumBits 32)
+endif()
+
+if ("${COMPRESSED_OBJECT_HEADER}" MATCHES "ON")
+  if (NumBits EQUAL "64")
+    set(LEAN_COMPRESSED_OBJECT_HEADER "#define LEAN_COMPRESSED_OBJECT_HEADER")
+    message(STATUS "Using compressed object headers, this feature assume the OS only uses memory addresses < 2^48")
+  else()
+    message(STATUS "Compressed object headers cannot be used in 32-bit machines")
+  endif()
+else()
+    message(STATUS "Using big object headers")
+endif()
+
 if ("${RUNTIME_STATS}" MATCHES "ON")
   set(LEAN_EXTRA_CXX_FLAGS "${LEAN_EXTRA_CXX_FLAGS} -D LEAN_RUNTIME_STATS")
 endif()
diff --git a/src/config.h.in b/src/config.h.in
index e5c4b871bd..7c2f3d8725 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -7,3 +7,4 @@ Author: Leonardo de Moura
 #pragma once
 @LEAN_SMALL_ALLOCATOR@
 @LEAN_LAZY_RC@
+@LEAN_COMPRESSED_OBJECT_HEADER@
diff --git a/src/runtime/lean.h b/src/runtime/lean.h
index b16f4a33de..7848975a67 100644
--- a/src/runtime/lean.h
+++ b/src/runtime/lean.h
@@ -15,9 +15,6 @@ Author: Leonardo de Moura
 #include <malloc.h>
 #endif
 
-#define LEAN_SMALL_ALLOCATOR
-// #define LEAN_COMPRESSED_OBJECT_HEADER
-
 #ifdef __cplusplus
 #include <atomic>
 #define _Atomic(t) std::atomic<t>
@@ -27,6 +24,7 @@ extern "C" {
 #include <stdatomic.h>
 #define  LEAN_USING_STD
 #endif
+#include "config.h"
 
 #define LEAN_CLOSURE_MAX_ARGS      16
 #define LEAN_OBJECT_SIZE_DELTA     8