diff --git a/ChangeLog b/ChangeLog
index 58c517879c..a44b8e6cc2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Jul 10 14:13:50 2011  Koichi Sasada  <ko1@atdot.net>
+
+	* internal.h (rb_thread_call_with_gvl, rb_thread_call_without_gvl):
+	  make them visible as experimental C APIs.  fixes Feature #4328.
+
 Sun Jul 10 12:18:00 2011  Kenta Murata  <mrkn@mrkn.jp>
 
 	* ext/bigdecimal/bigdecimal.c (BigDecimal_power): support non-integral
diff --git a/internal.h b/internal.h
index a5b9297c04..a6c633ba3f 100644
--- a/internal.h
+++ b/internal.h
@@ -164,7 +164,6 @@ struct timeval rb_time_timeval(VALUE);
 VALUE rb_obj_is_mutex(VALUE obj);
 VALUE ruby_suppress_tracing(VALUE (*func)(VALUE, int), VALUE arg, int always);
 void rb_thread_execute_interrupts(VALUE th);
-void *rb_thread_call_with_gvl(void *(*func)(void *), void *data1);
 void rb_clear_trace_func(void);
 VALUE rb_thread_backtrace(VALUE thval);
 VALUE rb_get_coverages(void);
@@ -199,8 +198,16 @@ void Init_prelude(void);
 #if defined __GNUC__ && __GNUC__ >= 4
 #pragma GCC visibility push(default)
 #endif
-VALUE rb_thread_io_blocking_region(rb_blocking_function_t *func, void *data1, int fd);
 const char *rb_objspace_data_type_name(VALUE obj);
+
+/* experimental.  these APIs can be changed. */
+VALUE rb_thread_io_blocking_region(rb_blocking_function_t *func, void *data1, int fd);
+
+void *rb_thread_call_with_gvl(void *(*func)(void *), void *data1);
+VALUE rb_thread_call_without_gvl(
+    rb_blocking_function_t *func, void *data1,
+    rb_unblock_function_t *ubf, void *data2);
+
 #if defined __GNUC__ && __GNUC__ >= 4
 #pragma GCC visibility pop
 #endif