diff --git a/src/musikcore/library/track/TrackList.cpp b/src/musikcore/library/track/TrackList.cpp
index 93e198dbf..8030422ea 100755
--- a/src/musikcore/library/track/TrackList.cpp
+++ b/src/musikcore/library/track/TrackList.cpp
@@ -278,9 +278,9 @@ void TrackList::CacheWindow(size_t from, size_t to, bool async) const {
     if (async) {
         currentWindow.Set(from, to);
         auto shared = shared_from_this(); /* ensure we remain alive for the duration of the query */
-        bool completionFinished = false;
-        auto completion = [this, &completionFinished, shared, from, to, query](auto q) {
-            if (completionFinished) {
+        auto completionFinished = std::make_shared<bool>(false); /* ugh... keep it alive. */
+        auto completion = [this, completionFinished, shared, from, to, query](auto q) {
+            if (*completionFinished) {
                 return;
             }
             if (query->GetStatus() == IQuery::Finished) {
@@ -296,7 +296,7 @@ void TrackList::CacheWindow(size_t from, size_t to, bool async) const {
                 this->CacheWindow(from, to, true);
             }
             this->WindowCached(const_cast<TrackList*>(this), from, to);
-            completionFinished = true;
+            *completionFinished = true;
         };
 
         this->library->EnqueueAndWait(query, kCacheWindowTimeoutMs, completion);
diff --git a/src/musikcube/cursespp/cursespp/InternalWindowMessages.h b/src/musikcube/cursespp/cursespp/InternalWindowMessages.h
new file mode 100644
index 000000000..d17cfd641
--- /dev/null
+++ b/src/musikcube/cursespp/cursespp/InternalWindowMessages.h
@@ -0,0 +1,48 @@
+//////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2004-2020 musikcube team
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+//    * Redistributions of source code must retain the above copyright notice,
+//      this list of conditions and the following disclaimer.
+//
+//    * Redistributions in binary form must reproduce the above copyright
+//      notice, this list of conditions and the following disclaimer in the
+//      documentation and/or other materials provided with the distribution.
+//
+//    * Neither the name of the author nor the names of other contributors may
+//      be used to endorse or promote products derived from this software
+//      without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+//////////////////////////////////////////////////////////////////////////////
+
+#pragma once
+
+namespace cursespp {
+    namespace InternalWindowMessages {
+        /* range of message ids reserved for internal use. exercise caution if
+        creating your own messages within this range. */
+        static const int kLastReservedMessageId = INT_MAX;
+        static const int kFirstReservedMessageId = kLastReservedMessageId - 1024;
+
+        static const int NotifyVisibilityChanged = kFirstReservedMessageId + 1;
+        static const int NotifyChildFocusChanged = kFirstReservedMessageId + 2;
+
+    }
+}