diff --git a/src/core/Mixer.cpp b/src/core/Mixer.cpp
index 14313505b..d7e93adc5 100644
--- a/src/core/Mixer.cpp
+++ b/src/core/Mixer.cpp
@@ -495,8 +495,7 @@ sampleFrameA * Mixer::renderNextBuffer()
 	MicroTimer timer;
 	static song::playPos last_metro_pos = -1;
 
-	song::playPos p = engine::getSong()->getPlayPos(
-						song::Mode_PlayPattern );
+	song::playPos p = engine::getSong()->getPlayPos( song::Mode_PlayPattern );
 	if( engine::getSong()->playMode() == song::Mode_PlayPattern &&
 		engine::getPianoRoll()->isRecording() == true &&
 		p != last_metro_pos && p.getTicks() %
diff --git a/src/core/ProjectRenderer.cpp b/src/core/ProjectRenderer.cpp
index 3ee3fad79..1633a4ec1 100644
--- a/src/core/ProjectRenderer.cpp
+++ b/src/core/ProjectRenderer.cpp
@@ -59,9 +59,9 @@ FileEncodeDevice __fileEncodeDevices[] =
         ".mp3", &AudioFileMp3::getInst },
 	{ ProjectRenderer::FlacFile,
 		QT_TRANSLATE_NOOP( "ProjectRenderer", "FLAC File (*.flac)" ),
-		".flac", 
+		".flac",
 #ifdef LMMS_HAVE_FLAC
-					&AudioFileFlac::getInst 
+					&AudioFileFlac::getInst
 #else
 					NULL
 #endif
@@ -219,7 +219,12 @@ void ProjectRenderer::run()
 #endif
 #endif
 
+	// have to lock Mixer when touching Song's state as the FIFO writer thread
+	// may call Mixer::renderNextBuffer() (which calls Song::doActions())
+	// simultaneously
+	engine::mixer()->lock();
 	engine::getSong()->startExport();
+	engine::mixer()->unlock();
 
 	song::playPos & pp = engine::getSong()->getPlayPos(
 							song::Mode_PlaySong );
@@ -239,7 +244,9 @@ void ProjectRenderer::run()
 		}
 	}
 
+	engine::mixer()->lock();
 	engine::getSong()->stopExport();
+	engine::mixer()->unlock();
 }