Index: src/modules/module-tunnel-source-new.c
===================================================================
--- src/modules/module-tunnel-source-new.c	(revision 30653)
+++ src/modules/module-tunnel-source-new.c	(revision 30654)
@@ -521,6 +521,12 @@
         pa_operation_unref(operation);
 }
 
+static void source_write_volume_cb(pa_source *s) {
+    /* A bit silly but this is to make sure we only access the server
+     * connection on the IO thread. */
+    source_set_volume_cb(s);
+}
+
 static int source_get_mute_cb(pa_source *s, bool *mute) {
     struct userdata *u;
 
@@ -701,6 +707,7 @@
     u->source->update_requested_latency = source_update_requested_latency_cb;
     pa_source_set_get_volume_callback(u->source, source_get_volume_cb);
     pa_source_set_set_volume_callback(u->source, source_set_volume_cb);
+    pa_source_set_write_volume_callback(u->source, source_write_volume_cb);
     pa_source_set_get_mute_callback(u->source, source_get_mute_cb);
     pa_source_set_set_mute_callback(u->source, source_set_mute_cb);
     pa_source_enable_decibel_volume(u->source, true);
Index: src/modules/module-tunnel-sink-new.c
===================================================================
--- src/modules/module-tunnel-sink-new.c	(revision 30653)
+++ src/modules/module-tunnel-sink-new.c	(revision 30654)
@@ -569,6 +569,12 @@
         pa_operation_unref(operation);
 }
 
+static void sink_write_volume_cb(pa_sink *s) {
+    /* A bit silly but this is to make sure we only access the server
+     * connection on the IO thread. */
+    sink_set_volume_cb(s);
+}
+
 static int sink_get_mute_cb(pa_sink *s, bool *mute) {
     struct userdata *u;
 
@@ -745,6 +751,7 @@
     u->sink->update_requested_latency = sink_update_requested_latency_cb;
     pa_sink_set_get_volume_callback(u->sink, sink_get_volume_cb);
     pa_sink_set_set_volume_callback(u->sink, sink_set_volume_cb);
+    pa_sink_set_write_volume_callback(u->sink, sink_write_volume_cb);
     pa_sink_set_get_mute_callback(u->sink, sink_get_mute_cb);
     pa_sink_set_set_mute_callback(u->sink, sink_set_mute_cb);
     pa_sink_enable_decibel_volume(u->sink, true);