diff --git a/ChangeLog b/ChangeLog
index 08f7ac2c64..2257af1268 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Mar 24 13:42:24 2013  Narihiro Nakamura  <authornari@gmail.com>
+
+	* gc.c (GC_ENABLE_LAZY_SWEEP): new macro to switch lazy sweeping
+	  for debugging. [Feature #8024] [ruby-dev:47135]
+
 Sun Mar 24 12:55:47 2013  Narihiro Nakamura  <authornari@gmail.com>
 
 	* gc.c: We have no chance to expand the heap when lazy sweeping is
diff --git a/gc.c b/gc.c
index 38bdcfd04b..253dc0afdd 100644
--- a/gc.c
+++ b/gc.c
@@ -98,6 +98,9 @@ static ruby_gc_params_t initial_params = {
 #ifndef GC_PROFILE_MORE_DETAIL
 #define GC_PROFILE_MORE_DETAIL 0
 #endif
+#ifndef GC_ENABLE_LAZY_SWEEP
+#define GC_ENABLE_LAZY_SWEEP 1
+#endif
 
 typedef struct gc_profile_record {
     double gc_time;
@@ -2043,7 +2046,7 @@ gc_prepare_free_objects(rb_objspace_t *objspace)
 {
     int res;
 
-    if (objspace->flags.dont_lazy_sweep) {
+    if (!GC_ENABLE_LAZY_SWEEP || objspace->flags.dont_lazy_sweep) {
 	if (heaps_increment(objspace)) {
 	    return;
 	}