diff --git a/src/libs/timeline/timelinerenderstate.cpp b/src/libs/timeline/timelinerenderstate.cpp
index 75238660729b6f45375a3587f10b05cda63617be..725946def7a10edc8e3ca4d82e7be386145bc643 100644
--- a/src/libs/timeline/timelinerenderstate.cpp
+++ b/src/libs/timeline/timelinerenderstate.cpp
@@ -29,6 +29,7 @@
 ****************************************************************************/
 
 #include "timelinerenderstate_p.h"
+#include <utils/qtcassert.h>
 
 namespace Timeline {
 
@@ -139,6 +140,8 @@ void TimelineRenderState::assembleNodeTree(const TimelineModel *model, int defau
                                            int defaultRowOffset)
 {
     Q_D(TimelineRenderState);
+    QTC_ASSERT(isEmpty(), return);
+
     for (int pass = 0; pass < d->passes.length(); ++pass) {
         const TimelineRenderPass::State *passState = d->passes[pass];
         if (!passState)