diff --git a/ChangeLog b/ChangeLog
index f41b3ebeaa..5615c44c5f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Tue Dec 29 06:50:42 2015  Eric Wong  <e@80x24.org>
+
+	* thread_sync.c: static classes
+
 Tue Dec 29 05:30:30 2015  Eric Wong  <e@80x24.org>
 
 	* lib/resolv.rb (Resolv::IPv6.create): avoid modifying frozen
diff --git a/thread_sync.c b/thread_sync.c
index 091246a7ad..9c73654b0f 100644
--- a/thread_sync.c
+++ b/thread_sync.c
@@ -1,7 +1,7 @@
 /* included by thread.c */
 
-VALUE rb_cMutex, rb_cQueue, rb_cSizedQueue, rb_cConditionVariable;
-VALUE rb_eClosedQueueError;
+static VALUE rb_cMutex, rb_cQueue, rb_cSizedQueue, rb_cConditionVariable;
+static VALUE rb_eClosedQueueError;
 
 /* Mutex */