diff --git a/ChangeLog b/ChangeLog
index 8d932256c3..0a7e377080 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Jun 15 17:48:42 2009  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* gc.c (os_obj_of): invoke garbage collection before iteration, to
+	  avoid accessing half recycled object references.  [ruby-dev:38613]
+
 Mon Jun 15 11:04:30 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* .gdbinit (rp, iseq): load dummy_gdb_enums on demand.
diff --git a/gc.c b/gc.c
index 74163bedb5..6d3c34e0bb 100644
--- a/gc.c
+++ b/gc.c
@@ -85,6 +85,7 @@ void *alloca ();
 int ruby_gc_debug_indent = 0;
 
 #undef GC_DEBUG
+#define GC_DEBUG
 
 /* for GC profile */
 #define GC_PROFILE_MORE_DETAIL 0
@@ -272,7 +273,7 @@ typedef struct RVALUE {
 	struct RComplex complex;
     } as;
 #ifdef GC_DEBUG
-    char *file;
+    const char *file;
     int   line;
 #endif
 } RVALUE;
@@ -2392,6 +2393,7 @@ os_obj_of(rb_objspace_t *objspace, VALUE of)
     RVALUE *p, *pend;
     volatile VALUE v;
 
+    rb_garbage_collect();
     i = 0;
     while (i < heaps_used) {
         while (0 < i && (uintptr_t)membase < (uintptr_t)heaps[i-1].membase)