diff --git a/ChangeLog b/ChangeLog
index 410c8d70ce..2c551530c7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Fri Jan 13 18:25:49 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* thread.c (rb_barrier_waiting): fix potential overflows.
+
 Fri Jan 13 17:23:38 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* load.c (load_unlock): update loading table at once.
diff --git a/thread.c b/thread.c
index d356cb5b36..cd7676364b 100644
--- a/thread.c
+++ b/thread.c
@@ -3687,18 +3687,18 @@ barrier_alloc(VALUE klass)
 #define GetBarrierPtr(obj) ((VALUE)rb_check_typeddata((obj), &barrier_data_type))
 #define BARRIER_WAITING_MASK (FL_USER0|FL_USER1|FL_USER2|FL_USER3|FL_USER4|FL_USER5|FL_USER6|FL_USER7|FL_USER8|FL_USER9|FL_USER10|FL_USER11|FL_USER12|FL_USER13|FL_USER14|FL_USER15|FL_USER16|FL_USER17|FL_USER18|FL_USER19)
 #define BARRIER_WAITING_SHIFT (FL_USHIFT)
-#define rb_barrier_waiting(b) ((RBASIC(b)->flags&BARRIER_WAITING_MASK)>>BARRIER_WAITING_SHIFT)
+#define rb_barrier_waiting(b) (int)((RBASIC(b)->flags&BARRIER_WAITING_MASK)>>BARRIER_WAITING_SHIFT)
 #define rb_barrier_waiting_inc(b) do { \
     int w = rb_barrier_waiting(b); \
     w++; \
     RBASIC(b)->flags &= ~BARRIER_WAITING_MASK; \
-    RBASIC(b)->flags |= (w << BARRIER_WAITING_SHIFT); \
+    RBASIC(b)->flags |= ((VALUE)w << BARRIER_WAITING_SHIFT);	\
 } while (0)
 #define rb_barrier_waiting_dec(b) do { \
     int w = rb_barrier_waiting(b); \
     w--; \
     RBASIC(b)->flags &= ~BARRIER_WAITING_MASK; \
-    RBASIC(b)->flags |= (w << BARRIER_WAITING_SHIFT); \
+    RBASIC(b)->flags |= ((VALUE)w << BARRIER_WAITING_SHIFT); \
 } while (0)
 
 VALUE